CS53091A2 - Solid thiocarbonate and method of its production - Google Patents

Description

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Solid thiourea and process for its production

Technical field

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of thiourea salts, in particular to a process for the preparation of thiocarbonate salts in solid form.

Background Art

Plant parasites, which significantly affect the plant's economic results, include helminths, which include over 10,000 species, of which at least 150 adversely affect plant growth. Plant parasitic helminths have been known since about 1750. Most of them cause crop loss by eating plant roots and occur predominantly in the upper few centimeters of soil predominantly on or near plants. They cause cecidia formation and swelling of the damaged parts of the roots by irradiating the roots, while greater contamination of the plant porosity by these parasites results in stunted plant growth, foliage fading, leaf wilting, and, in exceptional cases, even plant death.

Virtually all types of crops and ornamental plants can be attacked by parasitic helminths. Important nematode species are root helminths, which attack root roots and are hosted by tomatoes, alfalfa, ba-wool, grains, potatoes, citrus and other types of agricultural flats, as well as gold potato nematodes, beet cyst nematodes and citrus nematodes. These and some other helminth species are described in the "Soil Pest Review", published in Agri-cultural and Food Chemistry, Vol. 5, pp. 202-205 of 1955. infestation of a certain area of helminth, especially reduced resistance to bacteria and pathogenic soil fungi, with the exception of a small amount of soil that can be sterilized, but the possibility of destroying these harmful nematodes has not yet been found. , which enables economic economic activity, de-infection of soil with smoke, crop rotation with the inclusion of those varieties and species that are not host to parasites, and to a lesser extent breeding plants that are more resistant to infestation. it may be possible to reduce the occurrence of helminths by combining these techniques, with however, most of these restriction programs are relatively expensive.

Another problem of agriculture is the attack of plants by pathogenic microorganisms, especially fungi. Most often, these pathogens are destroyed by soil disinfection by smoke, by the cultivation of crops, by the use of a wide range of biocides and similar substances, most of which are not considered safe from an environmental point of view. Only a narrow spectrum of fungicides are cooked, but they are expensive and, over time, lose their effectiveness to other generations of fungi that have genetic adaptability.

The first of the known soil fumigants was carbon disulphide, which was used in Europe around 1870 to reduce the incidence of helminths in diabetes. However, this material is disadvantageous for practical use because it must be used in large quantities to compensate for the losses caused by its volatility. This material is also highly flammable and can eventually be ignited by static electricity, for example when spraying material or spilling it out of barrels. In addition, carbon disulfide has a very unpleasant odor and its fumes are toxic to humans. As a rule, carbon disulfide sold as a gaseous disinfectant is mixed with an inert flame-retardant composition such as carbon tetrachloride or other gaseous or smoke disinfectant. As a rule, these mixtures do not contain carbon disulphide in an amount greater than 20% by weight.

Carbon disulphide has been found to have a similar potency to insecticide as a disinfectant to soil, and can also be used as a rodent control or to control some species.

Many substances having nematocidal properties have already been developed, i.e., the ability to destroy nematodes, and contain as active ingredients, for example, polyamines, as shown in U.S. Pat. No. 9,979,454, heterocyclic compounds disclosed in U.S. Pat. No. 2,086,907, and various halogenated compounds . Useful nematocides containing halogens include 1,2-dibromoethane, methyl bromide, 5-bromopropine, 1,2-dichloropropane, ethylene dichloride and the like, all of which are phytotoxic, so their use for soil preparation is excluded.

One of the more significant commercial successes is 1,2-dibromo-5-chloropropane (DBCP), which can be used to eliminate helminths in the soil on which multi-planes are grown. However, the use of this substance has been limited by the discovery of adverse effects on the reproductive system of workers exposed to this chemical and it is believed that the substance also has carcinogenic effects. The non-usability of DBCP has been a serious obstacle for perennial plant growers, such as vine, stone fruit and walnut trees, since the cumulative growth of nematode populations is most pronounced in these plants, with most of the replacement soil disinfectants being very toxic to thyroid plants. Solutions associated with the use of DBCP as gaseous soil disinfectants are described in US-PS2,957,956 and 5,049,472.

Another class of materials used to control the occurrence of cucumbers is some thiocarbonates. U.S. Pat. No. 2,676,129 discloses the production of aliphatic disubstituted thioureas having the following composition:

wherein R 1 and R 8 are alkyl radicals having from 3 to 9 carbon atoms. These compounds are dissolved in acetone and added to the soils infested with helminths, which act to destroy these pests.

Other compounds are disclosed in U.S. Pat. No. 2,856,552 and 2,856,533, which are sodium and potassium trithiocarbonates, of which potassium trithiocarbonate belongs to the alkali metals and ammonium salts of tetrathioperoxicarbonate. According to the content of these patents, the two thio compounds are effective for reducing the occurrence of helminths.

These materials also state that all derivatives of n-thymus are effective as toxic substances for helminths. In addition, US-PS2 826 532 emphasizes that sodium trithiocarbonate has surprisingly better effects than potassium trithiocarbonate in functional acetocide.

Another serious problem with agriculture is the low usability of nitrogen for plant growth, since it has been found that agricultural crops use only 50 to 70% of nitrogen from the total amount of fertilizer that has been introduced into the soil. The greatest nitrogen losses are due to the fact that the nitrate and nitrite ions are extremely mobile in the soil environment and thus are easily lost by surface flushing and also by seepage from the roots of the plants to the deeper soil layers. Further losses of these ions are caused by denitrification, which is the reduction of elemental oxides of nitrogen or gaseous nitrogen oxides in the origin of the reduced uptake. In addition to significant economic losses, these nitrogen compounds represent a significant environmental pollutant, especially when flushed into surface or groundwater. Although some nitrogen is introduced into the soil in the form of nitrates, for example, ammonium nitrate, which is part of the fertilizer, most nitrogen fertilizers contain ammonia and ammonia compounds other than nitrate or urea materials. Ammonium nitrate is firmly bound by various physical and chemical processes in the soil, resulting in significantly smaller losses. Unfortunately, bound ammonium nitrate is also very poorly useful for plant growth.

The nitrification process leads to the conversion of ammonia ions into nitrate ions. Microbial species, known as nitrosomones, oxidize ammonia to nitrates while nitrobacteres oxidize nitrites to nitrates. These more moving ions are easily trapped by plant roots and are also easily assimilated by plants. In this respect, the nitrification process is desirable, but it has not yet been possible to control the rate of this conversion. Nitrification inhibition would result in the formation of nitrogen, which can be used by the plants in a longer period of time, thereby improving nitrogen absorption by the plants.

Numerous substances including expensive organic materials, for example 2-chloro-6-trichloromethyl-pyridine, 2-amino-4-chloro-6-methylpyrimidine, sulfathiazole, alkanolsulfathiazoles and the like have been proposed as nitrification inhibitors. J.M. Bremmer and G. L. Bundy in Soil Biology and Biochemistry, vol. 6, p.161-165 of 1974, describe the effectiveness of various volatile organic sulfur compounds, especially methylmercaptan, dimethylsulfide, dimethyl disulfide, carbon disulfide, and hydrogen sulfide. The carbon disulfide is said to have a noticeable slowing effect on nitrification in soil incubated in a closed system when selecting a very small amount thereof. Carbon disulfide was tested in the field, and the results are described in the article by J. Ashworta in the Chemistry and Industry magazine of September 6, 1975, pp. 749 and 75, and the test results indicate that carbon disulphide effects slow nitrification. U.S. Pat. No. 4,078,912 discloses the use of sodium, potassium and ammonium tritium bicarbonates to provide a means for slowing nitrification either alone or in fertilizer mixtures; the process describes how carbon disulphide is released from the mixture.

The chemistry of thiocarbonic acids and their salts was much more detailed, as can be seen from the works of O'Donoghua and Ka-Han in the Journal of Chemical Society, Vol.89 / II /> 19012-1818 of 1906, Yeoman in the Journal of Chemical. Society, Vol.119, pp. 58-54 of 1921, Mills and Robinson in Journal of Chemical Society, vol.128 / 11 /, pp. 2526-2552, and Stone et al. U.S. Pat. No. 2,895,855.

According to O'Donoghua and Kahan, 1826 derivatives of thiourea were prepared according to Berzell, which reacted aqueous solutions of hydrosulphides with carbon disulphide and formed non-stable solutions from which unstable crystalline salts were obtained according to the following reaction: 2 KSH + CS2 = K2CS5 + H2S / 2 /

Other thiocarbonates have also been prepared which are described in the work of Idoghu and Kahan. This article describes page 1818 preparation of ammonium thiosulphate by reacting liquid ammonia with cold alcoholic thiourea by dripping a calcium thiocarbonate solution into concentrated hydrochloric acid to prepare free thiourea acid. The calcium bicarbonate used has been described by the authors as a calcium salt containing calcium cations in combination with hydroxide. as well as thiourea anions. Other mixtures, such as sodium, magnesium, zinc, and lead salts, were also prepared in addition to free thiourea, according to O'Donoghu and Kahan. However, a common feature of all of these formulations was their relative instability, which was manifested by the decomposition of the mixture and the release of carbon disulfide and hydrogen sulfide and / or metal sulfide, which took place over several minutes. Yeoman's work describes the further study of thiocarbonates called trithiocarbonates in this work and also describes the preparation and properties of perthicarbonates or tetrathio-carbonates and tetrathio-carbonate derivatives of HgCS2. Yeoman also describes a process for producing ammonium salts, alkali metal salts and alkaline earth metal salts. For example, Yeoman prepared ammonium thiosulphate by saturating the alcoholic ammonia solution with hydrogen sulphide and then adding carbon disulphide to precipitate the resulting salt. Ammonium percarbonate was prepared in a similar manner, with the difference that elemental sulfur was added after the reaction of the ammonia with sulfur dioxide to form the disulfide NH4 / 2S2, with the addition of carbon disulphide to precipitate the final product.

Yeoman reports that the ammonium trithiocarbonate and pertharbonate solution is very unstable due to both decomposition to form the thiocyanate product and decomposition back to ammonia, carbon disulfide and hydrogen sulfide. An important explanation of the stability of thiocyanates, which has been elucidated by examples with sodium tri-thiosulphate and pertharbonate, is presented in this paper. Sodium trithio carbonate solution in water is considered stable only if oxygen and carbon dioxide are prevented; the presence of oxygen causes decomposition in which thiosulphide carbon disulphide is formed, while carbon dioxide decomposes the solution to form carbonate and carbon disulphide. Similarly, a perthium carbonate solution is considered stable for some time only in the absence of oxygen, with the presence of air causing decomposition of thiosulphate and carbon disulphide, the presence of carbon dioxide causing the mixture to decompose into carbonate, elemental sulfur, sulfur and hydrogen sulfide. According to Yeomanach, magnesium thioureas are similar.

Yeoman has also attempted to prepare the salts of thiourea and describe their stability with the four alkaline earth metals. Yeomen has not been able to prepare pure tri- or tetrathio-calcium carbonate, but has observed that the sodium or calcium trithiocarbonate salt which he has succeeded has been it was more stable than sodium or magnesium thiourea, probably because it was less hygroscopic. The Barnate salt of thiourea and tetrathiocarbonate cannot be isolated, although Yeoman believes there is a solution to this problem. It is also not possible to isolate solid barium tritium carbonate, although it is said to behave similarly to trithio-sodium carbonate dissolved in water. The preparation of aqueous solutions of tris- and tetrathium magnesium carbonate and strontium has been reportedly carried out, but the magnesium thiourea has not been isolated.

Said article of Mills and Robinson describes the preparation of ammonium thio-carbonate by leaching ammonium pentasulfide with sulfur-8 carbon. Ammonium pentasulfide was obtained by suspending the sulfur in the aqueous ammonia and then saturating it with hydrogen sulfide. The crystalline residues from this reaction were ammonium perthicarbonate. They prepared "better" the resulting ammonium percarbonate, but by extracting the ammonium pentasulfide with carbon disulfide in a Soxhlet device.

Stone, along with his team, describes several methods of preparing solid ammonia, alkali metal hydroxide, and alkaline earth metal salts of tri- and tetraperoxythioureas, which they later call simply tetrathiocarbonates. One of these processes involves dissolving the active metal, for example, hydrogen, in anhydrous ethanol to prepare ethoxide which reacts with hydrogen sulfide and carbon disulfide to sodium trithiocarbonate. However, these authors also report that trithiocarbonates have a tendency to dissolve in ethanol and to obtain a solid. material from the solution, it is necessary to treat the reaction mixture with a so-called transfer agent, for example ether, in which case thiocarbonates are often separated but not as solid particles but in the form of hardly crystallizing oils which can be saturated with aqueous solutions trithiocarbonate salts. Consequently, this process is not suitable for commercial use. Similar problems have been encountered in connection with tetra-thiocarbonate salts which have been prepared by a process similar to the preparation of trithiocarbonates.

These problems have been allegedly solved by the processing reaction in the medium, which is largely composed of non-solvent reactants and, to a lesser extent, a liquid that is susceptible to insoluble matter and which is a solvent for inorganic sulfides. The preferred non-solvent is a low-boiling hydrocarbon material such as hexane, cyclohexane, and benzene. The solvent was preferably ethanol, isopropanol or dioxane. Basic physical and chemical properties of these materials

The large number of processes for their preparation are summarized and explained in greater detail on pages 154-177 of Topicsin Sulfur Chemistry, Vol. 2, A. Senning, Editor, George ThiemePublishers, Stuttgart, 1977, in G. Gattow and W.Behrendt, "Carbon Sulfides and Their Inorganic and Complex Chemistry".

SUMMARY OF THE INVENTION

The drawbacks of this prior art are eliminated by the production of thiocarbonates in the form of thiocarbonic acid solid salts, and the invention also addresses stabilized thioureas; the principle of this process is that the stabilized aqueous solutions of thiourea salts are converted to solid carbonates by evaporation until drying. Such stabilized solutions are described in our earlier US-PA 07/262 961,07 / 262 962, 07/415 874 and 07/440 024, in which sulfides, polysulfides and / or bases are used to stabilize thiourea solutions.

Water is evaporated from the aqueous solution of the desired trithio-carbonate salt or tetrathiocarbonate containing a stabilizing amount of sulfide, polysulfide and / or base. In particular, a stabilizing amount of sulfide or polysulfide is used. In a most preferred embodiment, a stabilizing amount of the base with a sulfide or polysulfide is used. Evaporation may be carried out by boiling the solution under vacuum or by evaporation at normal pressure and at temperatures below boiling point. First, wet solid particles are produced which are then dried at elevated temperatures to produce the desired substantially dried solid. In a particularly preferred embodiment of the method according to the invention, the two operations are combined into a continuous process.

The requirement for the use of solid thiosulphate salts results from the fact that these salts are easier to transport and manipulate with, whereby the release of CS2 from these salts in the solid state is more easily controlled by various methods, e.g. adjuvants. Unlike aqueous solutions of thio-carbonate salts, which are essentially used after mixing the solution in water for spraying or irrigation, the carbonate salts in solid form are preferably used in agriculture where irrigation is not used. In this case, CS2 is liberated from the dusted solid thiosulphate by contact with water, for example with precipitation water. The basic advantages of the process according to the invention result from the comparison with the prior art methods for the production of solid thiourea salts, which require the use of organic solvents which are associated with environmental hazards. In contrast, the process of the invention does not require the use of organic solvents and does not endanger the environment. A further advantage of the process is that the " stabilized " solid thio-carbonates obtained by this process are more stable than the solids obtained by the previous methods and are therefore more useful as disinfectants for gaseous disinfection and for the preparation of other compositions containing thioureas, optionally for the preparation of "stabilized" thiourea solutions, described, for example, in US-A-07 / 262,961 and 07 / 262,962, by dissolving in water.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail with reference to the drawing, which shows a process diagram showing a system for carrying out the process according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Although aqueous thiocarbonate solutions are useful in a variety of applications, for example, to reduce the occurrence of helminths and other plant pathogens found in the soil or water, the use of thiocarbonate solutions has some disadvantages. Since aqueous thiourea solutions decompose by exposure to air, elevated temperatures or low pH of the environment, they must be kept in tightly closed containers before use. In addition, these solutions have a relatively short half-life of 11 after application to the soil.

It would therefore be desirable to provide thiocarbonates in a form which is easier to handle than aqueous solutions. We have found that a process for the production of solid thio-carbonates that does not require the use of organic solvents and which can be " stabilized " thiocarbonates which are more stable than solid thioureas known from the prior art and described, for example, in Mills, Robinson and Stone. In addition, these " stabilized " solid thiocarbonates are more suitable for a variety of uses including their use for disinfecting soil or liquid pest and insect pests, as well as animal pests that consume and / or deplete stored food and other articles and materials. The " stabilized " solid thiocarbonates described herein are more suitable than solid thioureas, known from the published literature, which are a semi-finished product for manufactured materials, for example, stabilized solid thiourea mixtures described by Pilling and Young in US-PA 07 (290992), the essential features of which are set forth herein.

Stabilized aqueous solutions of thiocarbonates from which stabilized solids can be obtained include aqueous solution of thiocarbonates and having the general formula of AgCS-1, wherein A is mono or divalent cation, b is 5 to 4? a is 2 when A is a monovalent cation, and aa is 1 when A is a divalent cation, and a base and / or sulfide and / or polysulfide of formula MnSx wherein M is selected from mono- and divalent cations, and the combination wherein x is at least 1, n is 2 when M is a monovalent cation, and n is 1 when M is a divalent cation. Aqueous solutions may contain mixtures of trithiocarbonate and tetrathiocarbonates having the same or different cations, as well as mixtures of sulfides and polysulfides with the same or different cations. Due to their availability and relatively low cost, suitable thioureas of ammonium thiourea, alkali earth thiocarbonates and alkaline earth metal thiosulphates and their combinations are preferred, with alkali earth thiocarbonates and alkaline earth thiocarbonates being most preferred. 12 "Stabilized solid" thiocarbonates are "non-stoichiometric" because they contain an excess of base and / or sulfide and because they are more stable under the action of water, air and / or increased temperature than solids prepared from aqueous or non-aqueous media and than stoichiometric "thiocarbonate mixtures, that is to say, mixtures containing only such amounts of carbon, sulfur and cationics, which correspond to the empirical formula for the corresponding tri-thiosulphates or tetrathiocarbonates, and not containing noticeable amounts of base and / or sulphide. The stabilized solid bicarbonates are stable in air at temperatures of about 24 ° C and at a relative humidity of 50% for at least 50 minutes, but generally at least 1 hour, preferably at least 2 hours, most preferably at least 6 hours, the stability being expressed by the time interval required to release 50% thiocarbonate equivalent of CS £ contained in the original solid. In these stabilized thioureas, a reduced tendency to absorb water from the atmosphere, to dissolve and oxidize it has been noted, as was the case with unstabilized solids, free of base and / or sulfide. The reduced moisture absorption manifests itself in a higher critical humidity for the stabilized solids, which is generally about 55%, preferably at least 50%, and most preferably at least 90%. Critical relative humidity is the relative humidity of the ambient air below which solids do not absorb water around their surroundings.

The stability of the solids in the air at a selected relative humidity and temperature can be readily determined by sorting the solid particles on a 50 mesh screen and allowing the sorted particles to remain in the selected conditions until the characteristic white color or time interval is changed. or until a certain amount of CS2 is released into the surrounding atmosphere. The loss of CS 2 can be determined by capturing the gaseous phase from the space around the sample and analyzing the gas for the carbon disulfide content. Similarly, the amount of CS2 equivalent remaining in the samples after the described stability test can be determined by dissolving the remaining portion of the solids in water, increasing the acidity to a pH of 4 or less of 13 - to dissolve the thiocarbonate and trapping the CS2 residue released in the toluene phase. covering the aqueous phase in which thiouphite is dissolved. The released CS2 is trapped in the toluene phase and its concentration can be determined by analyzing the toluene phase on the CS2 content of the gaseous chromatigraph.

The stabilized solids can be determined by their composition, that is, the amount of base and / or sulfide and / or polysulfide in the stoichiometric composition of thiocarbonate. The excess amount of base and / or polysulfide corresponds to at least 0.01, generally at least 0.02, preferably at least 0.04, and most preferably at least 0.08 equivalent amounts of base, sulfide or poly-sulfide to the equivalent amount of carbon disulphide in the solid thiourea .

In addition to the aforementioned advantages, the stabilized solid thiocarbonates have the additional advantage that, upon dissolution in water, they form stabilized thiocarbonate solutions which are described, for example, in US-A-07 / 262,961 and 07 / 262,962. containing the basic solution to the problem, further solved by the invention, stabilized aqueous solutions of thiocarbonates containing an excess of base, sulfide and / or polysulfide are much more resistant to decomposition of thiocarbonate and are therefore useful as disinfectants for gaseous disinfection as semi-finished products for further production and also have wide-spread bribes. The resulting stabilized solid thioureas can be used directly or can be dissolved in water or other solvents and used in agriculture or industry to find their application or where they are required. Thus, these solids or solutions prepared from solids can be used as gaseous disinfectants for sealed media, stored grain or other wasteful materials, or as soil disinfectants to reduce plant pests and parasite carriers such as nematodes. insects, fungi, bacteria, viruses and the like, whereby they can be applied to the leaf, to the soil surface or to other areas for destroying all kinds of pests. These solids can be introduced into 14-soil or fertilizer mixtures to slow down the non-encryption of ammonia fertilizers, as described in US-PA 07/128146, for dissolving paraffinic and / or bituminous deposits and for lowering the point of hydrocarbon and oil movement, as described in US-PA 07/222801, and may also be used for the production of lubricants for extraordinary pressures as described in US-PA 07/253 139 and 07/260 912. the stabilized aqueous solution of the thiosulphate salt is converted to a solid bicarbonate salt by a process comprising removing water from the stabilized aqueous solution of the bicarbonate salt. Since the thio-carbonate salt solution decomposes when exposed to significantly elevated temperatures, it is not possible to evaporate the thiocarbonate salt solution until a dried product is obtained at elevated temperatures. In addition, it is difficult and generally impossible to evaporate the stoichiometric thiocarbonate solution until it is completely dry, since it would be released and the resultant product would be an oil rather than a solid. Consequently, it is necessary to stabilize the solution using sulfides, polysulfides or bases, as will be described in more detail below.

The term "stabilized", which is used in relation to the aqueous solution, is to be understood as two basic aspects of the basic meaning of the term: chemical stability and physical stability, since the effectiveness of the mixture depends at least in large part on the carbon disulfide release capability during the process. For example, chemical stability can be quantified by chemical decomposition of the mixture and by measurement of the amount of carbon disulphide that is released, Alternatively, the amount of carbon disulphide can be determined by spectrophotometric determination of the presence of thiocarbonyl bond. The absorbance of the wavelengths corresponding to the wavelengths usually absorbed by the thiocarbonyl energy can be utilized for knotting analysis.

Physical stability is a sign of chemical stability, but it also has a separate meaning. This term is important for determining the nature of the products formed during decomposition of the mixture, especially ammonia, if present, hydrogen sulfide and carbon disulphide, all of which have a high vapor pressure. It will be appreciated that changing the physical form of the mixture from a low vapor pressure solution to a mixture of components, where a high vapor pressure occurs for each component, will be a requirement for storage vessels. Thus, vapor pressure above the composition of the invention can be used as an indicator of physical stability; the desired property of the composition of the invention is to maintain a low vapor pressure. Another indicator of physical instability is the formation of undesirable insoluble precipitates, which most often are sulfur, or immiscible liquid phases, for example carbon disulfide. A more general feature of physical stability is the presence of only one phase in the mixture *

Determination of the stability of the solution is based on the determination of both physical stability and chemical stability in a particular time period in which stability is required. Solutions of a particular composition do not form precipitates and do not release vapors in such a quantity as to increase vapor pressure during the average storage period, and are therefore more advantageous than substances of a different composition which have greater chemical stability but which exhibit undesirable physical changes during storage. .

The thiocarbonates which can be used include, without particular limitation, the salts of trithiourea and tetrathiocarbonate, the composition of which is expressed by empirical formulas corresponding to those of e.g. [NH 4] (gCS 2 ') NH 4 / gS. This mixture is generally soluble in water and can be prepared, stored and used in the form of an aqueous solution. The solutions are stable throughout the extended storage period in sealed containers, producing low vapor pressure and not flammable.

The stability of both concentrated and dilute thiourea solutions can be greatly enhanced with respect to CS release and physical stability by addition of base, sulfide and / or polysulfide. The increase in stability is particularly evident in more concentrated solutions, i.e., in solutions having equivalent CS2 concentrations in excess of 1% by weight. Aqueous solutions which can be stabilized by the addition of a base, a sulfide and / or a polysulfide include solutions of tri- and tetrathio-ammonium, alkali and alkaline earth metals and combinations thereof, wherein very stable solutions of alkali metal and alkaline metal tetrathiocarbonates can be obtained soil. Significantly increased stability can be achieved in more concentrated solutions. That is, a substantial increase in stability can be achieved in mixtures having a CS2 equivalent concentration of 1% by weight or even more than 5% by weight, with the increase reaching the solubility limit of thiocarbonate in solution. More concentrated solutions, in particular, have a thiocarbonate concentration corresponding to 1 to 20% by weight of carbon disulfide equivalent. The stability and safety of concentrates containing at least 10% by weight CS2 equivalent may be greatly enhanced by this process.

An increase in stability can be achieved by supplementing the solution with an organic or inorganic base, which is particularly soluble in the solution and which has particularly good water solubility. The bases used include water-soluble inorganic bases, and most preferably alkali metals and ammonium hydroxide, or combinations thereof. Alternatively, a similar increase in stability can be achieved by adding sulfides and / or polysulfides to the solution, which are particularly soluble in solution and preferably have good water solubility. Exemplary sulfides are ammonium sulfides and alkali metal and alkaline earth metal sulfides and polysulfides have the general formula MS wherein M is ammonium, alkali or alkaline earth metal, x is at least 1, especially greater than 1 in the case of polysulfides, and is from 1 to 5, most preferably at least 1 to 5, and n is 1 when M is an alkaline earth metal. Combinations of different sulfides and / or polysulfides may also be used. Combinations of ammonium sulfides, alkali sulfides and metal sulfides of α-17-calcium soils and / or polysulfides can also be used to stabilize thiourea mixtures, while further enhancing stability can be achieved using combinations of the bases, sulfides and / or polysulfides described. Most preferred stabilized thiocarbonate solutions contain a base added to the at least one sulfide or polysulfide described.

Any amount of base or sulfide added or a combination thereof increases the stability of the solution. Thus, useful mixtures include aqueous thiourea solutions containing added bases, sulfides and / or polysulfides. Generally, the amount of base, sulfide or polysulfide added is up to 0.01, in particular 0.02, and most preferably 0.04, and especially 0.08 equivalents of base, sulfide or polysulfide per equivalent of carbon disulfide in solution. Concentrated aqueous solutions of tetrathiocarbonates having a CSg vapor pressure corresponding to CS 2 concentrations in the equilibrium gas phase below about 1% at 24 ° C, i.e. below the carbon disulphide limit, can be achieved at a base concentration of about 0.02 equivalent of base per equivalent of carbon disulfide. A somewhat larger concentration of base, i.e. at least about 0.08 equivalents of base per equivalent of carbon disulfide, is suitable for the preparation of aqueous solutions of tri-thiocarbonates having a CSg partial pressure corresponding to at most 1% by volume of carbon disulphide at equilibrium gas phase at te - temperature 24 ° C. While a substantial improvement in solution stability and reduction of CS 2 partial pressure can be achieved by the use of sulfides and / or polysulfides without the addition of a base, the concentration of sulfides and / or polysulfides required to achieve the desired CSg partial pressure and consequently to increase stability is somewhat higher than the concentration. principles, a similar increase in stability is needed. Therefore, to achieve a CSg partial pressure of »corresponding to a CSg concentration at equilibrium gas phase above the solution of less than 1% by volume at 24 ° C, the preferred use of sulfide and / or polysulphide concentrations of about 0.04 equivalents of sulphide and / or polysulphides per carbon disulfide equivalent As in the case where the base was added, greater stability of the solution and lower pressure CS2 can be achieved by using even greater concentrations of sulfides and / or polysulfides, or by using base combinations with sulfides and / or polysulfides. The concentration of sulfides, polysulfides or combinations thereof should be at least about 0.02, especially at least 0.04, and most preferably at least 0.08 equivalent amounts of sulfide and / or polysulfides per equivalent amount of carbon disulfide. However, when a combination of base and sulfide is used, the respective concentrations of each component should be reduced to about half in order to achieve a comparable degree of improvement in stability and reduction of CS2 partial pressure. In other words, the degree of stability enhancement achieved by using 0.02 equivalent of base per equivalent of sulfur-carbon can be achieved using about 0.01 equivalent of the base in combination with about 0.01 equivalent of n-sulfide n-sulfide. The term "equivalent" in this case is used in its conventional sense, so that one mole of carbon disulfide forms 2 equivalents and the same applies to sulfide and polysulfide, and to alkali earth metal bases and other bases that are useful for cation. one mole of ammonium bases and alkali metal bases, the cation of which is monovalent, represents only 1 equivalent, therefore, on a molar basis, as opposed to the equivalent base, 2 moles of alkali metal hydroxide, for example sodium hydroxide, correspond to 1 mole of carbon disulfide .

The amount of sulfide and / or polysulfide base should be sufficient to reduce the carbon disulfide partial pressure of the desired value, and the added amount of additives required to achieve the desired effect can be readily determined by the addition of various known amounts of base, sulfide and / or polysulfides to the thiosulphate solution at maintaining a space above the vapor collection solution at a temperature of 24 ° C for a sufficient period of time, for example 24 hours, and analyzing the gas phase by a gas chromatograph to determine the carbon disulphide content. The lower additive concentrations exhibit a somewhat higher equilibrium concentration CS2 and also the higher partial pressure of CS2 &apos;, while higher concentrations of additives manifest themselves in lower partial pressure CS2. 19 -

Most preferred blends are those in which the carbon disulphide partial pressure has been reduced to a level of about one volume percent or less of carbon disulfide in the equilibrium gas phase at 24 ° C. A larger safety factor with regard to partial pressure CS2, toxicity, handling difficulty and the like can be achieved by limiting the partial pressure CS2 at the lowest value. Most preferred thiocarbonate solutions are those in which the carbon disulfide partial pressure is less than 0.5 and most preferably less than 0.2 vol. Carbon disulphide in equilibrium gas phase over the solution at 24 ° C.

Bases containing bases and having increased stability can be readily obtained by adding the desired amount of thiocarbonate salt solution base. The base may be added before, during or after the preparation of the thiocarbonate salt solution, it is only necessary that the resulting mixture contain an added base, preferably the base is added during or after the preparation of the thiourea salt solution. Similar techniques can be used to prepare mixtures containing a sulfide polysulfide. That is, soluble sulfides or polysulfides can be added before, during or after the preparation of the thiocarbonate salt solution, and the addition of sulfides during or after the preparation of the thiocarbonate salt solutions is preferable. The sulfide and polysulfide may be incorporated into the mixture by the direct addition of this component or may be formed at the site. The required amount of base, for example potassium hydroxide, can then be added by adding an equivalent amount of sulfur hydrogen to convert the base to the corresponding sulphide, to sulphurous potassium KgS. The polysulfides may be formed in situ by the addition of elemental sulfur with appropriate agitation to promote elemental sulfur reaction with the sulfide already present in the mixture.

The process of the invention removes water from an aqueous solution of thiocarbonate salts that has been stabilized against loss of CS 2. Water is removed by treating the mixture at a temperature sufficient to vaporize water from a solution without excess decomposition of thiourea salts, with the decomposition of these salts resulting in loss of CS £ from salt. This process according to the invention is carried out by evaporating the stabilized thiocarbonate solution at temperatures below the boiling point of the solution or by boiling a stabilized solution of the thiocarbonate salt in a sufficiently large container to prevent decomposition of the salt at a more pronounced scale.

The evaporation process or the vacuum distillation process which satisfies the above conditions are useful for carrying out the process according to the invention. In particular, vacuum evaporation is used to vaporize water from a stabilized thiocarbonate solution since the thiocarbonate has a relatively low critical temperature at which it decomposes. However, other processes may also be used to produce a dried thiocarbonate containing a substantial amount of bound CS2. The stabilized aqueous solution may also be vaporized at normal temperature and pressure of the atmosphere by simple and free evaporation of water from the air. This means that a vacuum can be created around the solution and / or the solution can be heated to a temperature that does not decompose thiourea. The term "thiourea excess" is used herein in the sense that there should be no such extensive decomposition of the solid thiocarbonate in a stabilized solution, which would result in a marked decrease in the solid thiocarbonate in solution as a result of the evaporation process.

The process of the invention will be explained in more detail in the production of potassium tetraathiocarbonate, and similarly in other thiocarbonates. The decomposition point of the potassium solid carbonate determined in the melting point detection device is about 30 ° P, i.e. about 150 ° C. The boiling point of the thiourea aqueous solution varies depending on the concentration and pressure. For example, a 40% potassium thiocarbonate solution at 68 ° C at a vacuum of about -635 mm Hg while boiling at normal atmospheric pressure is about 101 ° C. In general, at atmospheric pressure, the boiling point is about 15 ° C higher than under vacuum -635 mm Hg. 80% by weight of the saline solution is boiled at about 90 ° C in a vacuum of -635 mm Hg 21 and at a temperature of about 123 ° C at atmospheric pressure. Distillation of water from a solution of potassium thiosulphate in a vacuum of about -635 mmHg gradually raises the temperature to 93 ° C. · The resulting hoses are wet to the touch and tend to form cakes.

Drying of this non-collapsing material can be carried out at ambient pressure by means of a rotary dryer, a spray dryer, or in evaporation or low temperature furnaces. The dry solid is formed at atmospheric pressure at elevated temperature to 132 ° C to 145 ° C. · Tetra-thiourea starts to decompose at temperatures above 148 ° C.

Vacuum drying with a vacuum of -635 mm Hg or less is preferable because the drying of the stabilized thiocarbonate salt solution in water under vacuum results in a dry solid thio-carbonate salt at temperatures substantially lower than the thermal decomposition of the salt. For example, in a vacuum of -635 mmHg, the dry solid is formed at a temperature of 98 ° C to 110 ° C. Vacuum drying is preferably carried out in a paddle mixer, a screw mixer or a rotary mixer.

The process of the invention will now be explained in detail with reference to the drawing, which illustrates a system for preparing solid thiourea salts by a intermittent or semi-continuous process.

The system includes a liquid storage tank 10 coupled to a feed pump 12 via an inlet pipe 14. The feed pump 12 is connected by its outlet side via a feed pipe 18 to a liquid distributor 16. The fluid distributor 16 is located inside the rotary dryer 20 and forms a needle portion, the rotary dryer 20 being provided with a heating jacket 22. The rotary dryer 20 is connected to a heat exchanger 24 acting as a condenser by a conduit 26, the exchanger 24 being connected by a second connecting conduit 30 to a vacuum condenser 28 to which a condensing pump 52 is connected by a third conduit 34. A blower 56 is connected to the vacuum collector 28 by a fourth conduit 58 and a valve 40 is inserted in the fourth conduit 58. The blower 56 is connected to a vacuum pump (not shown) by a second valve 42 and a fifth connecting conduit 44. The blower 56 is bridged. By a bypass line 46 provided with a third valve 48, it is connected via a fourth valve 50 to a gas heater 52 by means of a sixth connecting conduit 54 from which the branch line 58 branches off with the fifth valve 56 to an inert gas source (not shown). The gas heating unit 52 is connected to the gas inlet 60 of the rotary dryer 20 by means of a seventh connecting line 62. The rotary dryer 20 is rotatable and can be rotated in the direction of the arrow 64. In an alternative embodiment, the rotary dryer 20 may be replaced by a stable stationary container provided with an inside rotating mixing elements. The gas outlet 66 of the rotary dryer 20 is connected to the first connecting pipe 26. The internal rotary dryer 20 is shown by the spray nozzles 68 provided on the liquid distributor 16, the solid product layer 70 and the grinding elements 72 mixed with the solid product particles 70. The starting material for carrying out the process of the present invention are thiocarbonate salt solutions having a concentration of from 15 to 80% by weight of thiocarbonate, in particular from 50 to 60% by weight of thiosulphate. Although magnesium tetrathiocarbonate has been mentioned explicitly in the foregoing example, it is to be understood that other thiocarbonates can also be treated, for example, ammonium tri-thiocarbonate and ammonium tetrathiocarbonate, and other alkali metal or alkaline earth metal thiosulphates or other thiourea salts.

In order to ensure that excess CS2 is not released during evaporation of the thiocarbonate salt solution and that water begins to evaporate instead of it, it is preferable to prepare the most aqueous solution. Stabilization can be accomplished by addition of a thiocarbonate with a base, a soluble sulfide salt or a polysulfide. The use of excess sulfide and base during the preparation of aqueous solutions of thiocarbonate salts is based on the operations already described in US-PA 415 874 and 440 024. In the process according to the invention, the aqueous solution is stabilized. thiourea salts, for example K 2 CS 4, are pumped from the storage tank 10 and sprayed in the rotary dryer 20 with the liquid distributor 16. The rotary dryer 20 is maintained at the desired temperature by means of a heating jacket 22 which increases and controls the temperature of the KgCS2 solution in the rotary dryer 20. During evaporation and drying, the water vapor from the KgCS2 is discharged to the heat exchanger 24 where they condense and condensate is drawn off through the second conduit 30 to a vacuum collector 28 from where it is pumped out by a condensing pump 32. The non-condensable gas or gases are passed by bypass around the blower 36 through a fourth conduit 38, bypass conduit 46 and an open valve 48 to the second valve 42 , which is also opened and through which gases flow to the vacuum pump and are removed. The first valve 40, the fourth valve 50 and the fifth valve 36 are closed during this intermittent process. During the evaporation and drying process, the rotary dryer 20 is rotated in the direction indicated by arrow 64. The grinding elements 72, which may be selected as needed, for example, from such comminution bodies as ceramic alloy balls, are added in order to avoid sticking the particles together or adhering the dried material to the walls of the rotary dryer 20. If necessary, the inside of the rotary dryer 20 may be provided with internal wiping means or knives to maintain the heat transfer surface of the wall dryer 20 or in an alternative an embodiment stationary box without stuck solid particles. Instead of the vacuum evaporation and drying process described above, a process using an inert gas such as nitrogen as a heating agent can also be used. In this alternative process, the solution of the stabilized thio-carbonate salt in water, e.g. is pumped into the storage container 10 and sprayed in the interior of the rotary dryer 20 by means of a liquid distributor 16. The rotary dryer 20 is maintained at the desired temperature by the heating jacket 22 and the gas firing unit 52 to control the temperature of the inert gas entering the rotary dryer 20 through the gas inlet 60. The intensity of the spray solution in the rotary dryer 20 controls the rate of water evaporation from the solution and storing the solids in the solids storage medium within the rotary dryer 20. Not only does the introduction of inert gas into the rotary dryer 20 prevent ingress of the inert gas, but also the removal of water vapor from the rotary dryer 20 through the outlet 66 and the connecting pipe 26 of the heat exchanger 24. The water vapor released from the K2CS4 solution during the evaporation and drying process condenses the heat exchanger 24 and passes through the second connection line 30 to the vacuum collector 28 from where the condensate is pumped out by the condensation pump 32. The inert gas passes through the blower 36 The fourth valve 50 returns to the gas firing unit 52. During this process, the second valve 42, the third valve 48 and the fifth valve 56 are closed. In addition, if desired, the inert gas may be passed through the fifth valve 56. A combination of both of these processes is also preferred. In such a combined process, the vacuum is used to vaporize the water vapor from the thiosulphate solution and the inert gas is used to dry the solids.

The solid bicarbonate salts prepared by the process of the invention may be slightly hygroscopic. In such a case, and in particular at high ambient humidity, the solid products are preferably loaded into suitable containers which are sealed after drying.

Accordingly, the process of the present invention provides for the production of solid bicarbonate acids without the use of organic solvents, and in providing conditions to avoid decomposition of thiourea salts.

The method according to the invention can be carried out with some variations which do not differ from the basic idea of the invention and its basic characteristics. For example, as discussed above, other than the rotary dryer 20 may be used to vaporize water from aqueous thiourea solutions used as starting materials to carry out the process of the invention. In particular, the described embodiments of the invention are intended to illustrate the invention but do not limit the scope of the invention as set forth in the claims.

Claims (35)

What is claimed is: 1. A process for producing a solid thiourea salt, wherein the stabilized aqueous solution of thiourea salt is evaporated to dryness. , 2. A process according to claim 1, wherein the salt is selected from the group consisting of ammonium trithiocarbonates, ammonium tetrathiocarbonates, alkali metal trithiocarbonates, alkali metal tetrathiocarbonates, alkaline earth metal trithiocarbonates and alkaline earth metal tetrathiocarbonates. 3. The process of claim 1 wherein the solution comprises from 15% to 80% by weight of thiourea salt. 4. The process of claim 1 wherein the solution comprises from about 30% to about 60% by weight of thiourea salt. 5. A process according to claim 1 wherein the solution comprises a stabilizing amount of admixture selected from sulfides, polysulfides, bases and mixtures thereof. 6. A process according to claim 5 wherein the stabilizing amount is at least 0.01 equivalent to the carbon disulfide present in the thiourea salt. 7. A process according to claim 5 wherein the stabilizing amount is at least 0.08 equivalent to the carbon disulfide present in the thiourea salt. 8. The process of claim 2 wherein the solution comprises a stabilizing amount of the additive selected from sulfides, polysulfides, bases and mixtures thereof. 27 - 9. A process according to claim 4 wherein the solution comprises a stabilizing amount of the additive selected from sulfides, polysulfides, bases and mixtures thereof. 10. A process for the production of a solid salt of thiourea, characterized in that it is stabilized in aqueous form. . the thiourea salt solution is evaporated and water is removed therefrom, whereupon the solid obtained by the evaporation process is dried, the solution being previously stabilized with a stabilizing amount of an additive selected from sulfides, polysulfides, bases and mixtures thereof . 11. The process of claim 10 wherein the solution comprises a stabilizing amount of a sulfide or polysulfide mixture and a base. 12. The process of claim 10 wherein the stabilizing amount is at least 0.01 equivalent equivalent of carbon disulfide present in the thiourea salt. 13. The process of claim 10 wherein the stabilizing amount of the additive is at least 0.08 equivalents per equivalent of carbon disulfide present in the thiourea salt. 14. The process of claim 10 wherein the evaporation is carried out at boiling in vacuo. 15. The process of claim 10 wherein the evaporation is carried out at ambient air pressure at a temperature below the boiling point. 16. The process of claim 10 wherein the drying operation is carried out by heating the resulting solid to an elevated temperature. 28. The process of claim 16 wherein the elevated temperature is a temperature above ambient air but less than the decomposition temperature of the thiourea salt. 18. The method of claim 10, wherein the evaporation operations and the drying operations form a semi-continuous process 19. The process of claim 10 wherein the evaporation operation is carried out under vacuum and the drying operation is carried out at ambient air pressure. 20. The process of claim 10 wherein the evaporation and drying are carried out in vacuo. 21. The method of claim 12, wherein the evaporation operation and the drying operation are performed at ambient air pressure. 22. The method of claim 14 wherein the vacuum is at least -625 mm Hg. A method according to claim 19, wherein the vacuum is at least -625 mm Hg. 24. The method of claim 20 wherein the vacuum is at least -625 mm Hg. 25. The process of claim 1 wherein the salt is potassium tetrathiocarbonate. 26. The process of claim 5 wherein the salt is potassium tetrathiocarbonate. 27. The process of claim 7 wherein the salt is potassium tetrathiocarbonate. 28. The process of claim 10 wherein the salt is potassium tetrathiocarbonate. - 29 - 29. The process of claim 13 wherein the salt is potassium tetrathiocarbonate. 30. The process of claim 1 wherein the solution has a CS2 partial pressure corresponding to at most 1% by volume of CS2 at equilibrium gas phase at 24 ° C. 31. The process of claim 1 wherein the solution has a CS2 partial pressure corresponding to at most 0.2% by volume of CS2 in equilibrium gas phase at 24 ° C. 32. The process of claim 10 wherein the solution has a CS2 partial pressure corresponding to at most 1% by volume of CS2 at equilibrium gas phase at 24 ° C. 33. The method of claim 10 wherein the solution has a CS2 partial pressure corresponding to at most 0.2% by volume of CS2 in equilibrium gas phase at 24 ° C. A process for the preparation of a solid thiourea salt by evaporating a stabilized aqueous solution of a thiourea salt selected from the group consisting of ammonium trithiocarbonate, ammonium tetrathiocarbonate, alkali metal trithiocarbonates, alkali metal tetrathiocarbonates, alkaline earth trithiocarbonates alkaline earth tetra-thiosulphates containing a thiourea salt in an amount of from 30% to 60% by weight, wherein the solution is stabilized with at least 0.01 equivalent of a selected group of sulfides, polysulphides, bases and mixtures thereof to the carbon disulphide present in the salt wherein the CS2 partial pressure solution is less than 1% by volume of CS2 in equilibrium gas phase at 24 ° C and drying is the result of an evaporation operation. 35. The process of claim 34 wherein the evaporation and drying operations are performed at ambient air pressure. - 50 - 36. The method of claim 34, wherein the evaporation operation and the drying operation are carried out under a vacuum of at least -625 mm Hg. 37. Stabilized solid thiourea produced according to paragraph 10. 38. A stabilized solid thiourea of the empirical formula A &amp; CS4 and a stabilizing amount of an additive selected from the group consisting of bases, sulfides, polysulfides, and combinations thereof, wherein A is selected from monovalent and divalent cations, b is 3 to 4, a is 2 if A is a monovalent cation and a is 1 if A is a divalent cation. A method for controlling the occurrence of pests, characterized in that a mixture comprising stabilized solid bicarbonates according to item 37 is applied to the area where the pests occur. 40. A method for controlling the occurrence of pests, characterized in that a mixture comprising stabilized solid bicarbonates according to item 38 is applied to the area where the pests occur or passes through them. 41. A method for controlling the occurrence of pests in soils, comprising introducing into the soil a mixture comprising stabilized solid thioureas according to clause 37. 42. A method for controlling the occurrence of pests in a soil, comprising introducing into the soil a mixture comprising stabilized solid thioureas according to item 38.