DE2635280A1 - Aliphatic mono-isocyanate prodn. - by reacting carbamoyl chloride and active hydrogen cpd., then thermal decomposition, of the adduct - Google Patents

Abstract

Prepn. of isocyanates of formula R-NCO (I) (R = 1-4C aliphatic hydrocarbyl, opt. olefinically unsatd) comprises reacting the carbamoyl chlorides RNH. COC1 (II) with cpds. contg. >=1 active H atom, in an inert solvent. HCl is eliminated during the reaction and an addition cpd. of (I) with (III) is formed. This adduct is then decomposed by heating to give (I) and (III) which are sepd. simultaneously by distn. Pref. (III) are amides of sulphuric acid or of organic sulphonic acids contg. the gp. -SO2NHR1 (R1 = aliphatic hydrocarbyl); phenols having >=1 electrophilic substit. to increase the acidity of the OH gp; or organic cpds. with >=1 -NH.CO.O-function. (I) re intermediates for plant-protection agents and pharmaceuticals. Reserve reaction between HCl and (I) is completely prevented, so high yields of high purity (I) are achieved without large investments in condensers etc.

Description

Process for the preparation of aliphatic

Monoisocyanates The invention relates to an improved process for the production of aliphatic monoisocyanates from the corresponding carbamic acid chlorides.

Isocyanates are known to be produced by reacting amines with phosgene manufactured. The reaction proceeds via the stage of the carbamic acid chlorides, the at higher temperatures split into the corresponding isocyanates and hydrogen chloride. If the boiling point of the isocyanate to be produced is well above the decomposition temperature of the carbamic acid chloride, the hydrogen chloride formed during the decomposition can problem-free especially when using an inert organic solvent be removed from the reaction space. However, if the decomposition temperature of Carbamic acid chloride is near or above the boiling point of the isocyanate, so the isocyanate gets into the gas space, where it with the hydrogen chloride to carbamic acid chloride recombined.

Therefore the split is imperfect; the isocyanate will only obtained in low yield and contaminated with carbamic acid chloride.

The situation described applies to aliphatic monoisocyanates to whose aliphatic radicals contain 1 to 4 carbon atoms, with the difficulties are greatest in the production of methyl isocyanate.

Numerous methods are described in the patent literature which to eliminate the difficulties mentioned. Much of the procedure describes the cleavage of carbamic acid chlorides using hydrogen chloride acceptors.

It is known to use isocyanates from carbamic acid chlorides in the presence of organic bases (e.g. tertiary amines) or carboxylic acid dialkylamides (DT-OS 1,593,554) or tetraalkyl ureas (U.S. Patent 3,644,461) in organic solvents to manufacture. Furthermore, the use of Water (DT-AS 2 156 761) and of aqueous solutions or suspensions -inorganic vasen (GB-PS 1 208 862). Olefins are also used as acceptors of hydrogen chloride called (DT-OS 2 210 285).

All of the processes mentioned have the serious disadvantage that By-products arise (corrosive organic or inorganic salts or alkyl chlorides), which either have to be reconditioned in a costly manner or are harmful to the environment represent.

In addition, there is a risk when using organic bases of side reactions to di- and trimeric isocyanates. In the presence of water a considerable part of the carbamic acid chloride is hydrolyzed to the amine hydrochloride, so that only in the case of the inert tertiary butyl isocyanate good yields be achieved.

Also the production of low-boiling aliphatic monoisocyanates by thermal cleavage of carbamic acid chlorides in organic solvents using special process techniques is known.

According to DT-AS 1 193 034 the thermal cleavage of the carbamic acid chloride is carried out in a reactor provided with a reflux condenser and a separating column. Hydrogen chloride escapes through the reflux condenser, while isocyanate and carbamic acid chloride escape and solvents are retained. The isocyanate formed ends up in the Column and can be removed at the top of the column. Through a return divider is most of the isocyanate is recycled, thus ascending into the column Hydrogen chloride is completely absorbed and in the form of carbamic acid chloride returned to the reactor.

When this process is carried out continuously, carbamic acid chloride is used depleted solution continuously withdrawn from the reactor, elsewhere with carbamic acid chloride enriched and fed back into the reactor.

In the German Offenlegungsschriften 2 411 441, 2 411 442 and 2 422 271 process variants are described which are based on the procedure mentioned in the above are based on the principle given and only have changes in equipment as their content.

Although the processes mentioned, the production of low-boiling aliphatic monoisocyanates by thermal cleavage of carbamic acid chlorides enabled, but serious disadvantages are also to be mentioned here: 1. The separation of hydrogen chloride requires reflux condensers with large cooling surfaces, which are more energy-intensive Way must be operated with refrigerants, so isocyanate and carbamic acid chloride be withheld quantitatively.

2. For the separation of carbamic acid chloride-free isocyanate by distillation Highly efficient fractionating columns are required from the reaction mixture, with a high reflux ratio must be set.

3. The procedures can only be carried out cheaply if proportionately dilute carbamic acid chloride solutions (1 to 30%) can be used.

4. In the case of continuous implementation (on an industrial scale only one in question) the reaction solution must be circulated several times.

All of this has the consequence that the reaction components (isocyanate, carbamic acid chloride and solvent) evaporated and condensed or cooled several times in the process and have to be reheated, which causes high energy consumption will. From the use of dilute solutions and the need for many cycles the result is a long residence time and thus a low space-time yield.

Due to the long residence time, there is a risk of a reduction in yield by trimerization of the monoisocyanate. The process requires a lot of effort of measurement and control technology. From this, from the low space-time yield and the The need for the use of highly efficient fractionation columns arises for technical production is a high investment.

The present invention now provides a completely new possibility opened, low-boiling aliphatic monoisocyanates from the corresponding carbamic acid chlorides to produce in good yields without major expenditure on equipment, with a Recombination remains completely excluded from hydrogen chloride with formed monoisocyanate.

The new principle on which the present invention is based exists therein, the carbamic acid chlorides having at least one active hydrogen atom Compounds with splitting of hydrogen chloride to form adducts of the desired monoisocyanates implement and then these adducts thermally into the desired monoisocyanate and the at least one active hydrogen atom used as auxiliary Split back connection. Simultaneously with this thermal cleavage of the adducts the cleavage products are separated by distillation.

In this way it is possible to obtain the hydrogen chloride from the carbamic acid chlorides quantitatively in a short time without the need for equipment and in pure form at a lower level Remove temperature from the reaction mixture, with the recombination of isocyanate and hydrogen chloride to carbamic acid chloride cannot enter because the isocyanate completely added to the resource used. Then the carbamic acid chloride-free cleaves Addition compound at a higher temperature again, and the released isocyanate can be isolated quickly and in pure form by distillation without any problems.

The present invention is therefore a method for Preparation of monoisocyanates of the formula R-NCO in which R is optionally olefinically unsaturated aliphatic hydrocarbon radical with 1 to 4 carbon atoms stands, from the corresponding carbamic acid chlorides of the formula R-NH-CO-Cl thereby characterized in that the carbamic acid chlorides in the presence of under the reaction conditions inert solvents with at least one active hydrogen atom containing compounds with elimination of hydrogen chloride to form addition compounds of the isocyanates R-NCO subsequently converts the addition compound thermally into the desired isocyanate RkiCO and the compound having at least one active hydrogen atom decomposed, whereby at the same time the monoisocyanate formed is distilled from the at least separating a compound having an active hydrogen atom.

The starting compounds for the process according to the invention are carbamic acid chlorides the formula R-NH-CO-Cl in which R is optionally olefinic unsaturated aliphatic hydrocarbon radical with 1-4 carbon atoms. In particular, R can represent a methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, or propenyl group. Preferably R stands for a methyl group.

Such carbamic acid chlorides are formed by reacting the corresponding ones Amines R-NH2 with phosgene with elimination of hydrogen chloride. The carbamic acid chlorides can also be used in a mixture with up to equimolar amounts in the process according to the invention are used on the corresponding monoisocyanates R-NCO. Such carbamic acid chloride-isocyanate mixtures arise through partial thermal elimination of hydrogen chloride from the corresponding Carbamic acid chlorides.

In the process according to the invention, the carbamic acid chlorides or the carbamic acid chloride-isocyanate mixtures preferably in 5 to 50 percent by weight Solutions in organic solvents which are inert under the reaction conditions are used.

The following solvents can be used, for example: Aliphatic hydrocarbons such as pentane, hexane, heptane, octane, cyclohexane, halogenated aliphatic hydrocarbons such as methylene chloride, chloroform, carbon tetrachloride, n-propyl chloride, n-butyl chloride and isomers, amyl chloride, cyclohexyl chloride, ethylidene chloride, dichloroethylene, ethylene chloride, Dichloropropane, dichlorobutane, 1 sopropyl bromide, n-propyl bromide, butyl bromide, ethyl iodide, Propyl iodide and fluorinated or partially fluorinated compounds; aromatic and substituted aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene, Chlorobenzene, dichlorobenzene, fluorobenzene, difluorobenzene, nitrobenzene, aromatic ether; Naphthalene derivatives such as chloronaphthalene; Ketones such as acetone, methyl ethyl ketone, Diethyl ketone, acetophenone; Esters such as ethyl formate, alkyl acetate, Propionic acid esters, phthalic acid esters, and other high-boiling esters; other organic Compounds such as carbon disulfide, methyl tert-butyl ether, ethyl propyl ether, Tetrahydrofuran, acetonitrile. Mixtures of the above can of course also be used Solvents are used. Chlorobenzene and / or ethylene chloride are preferred used.

At least one active one which is suitable for the method according to the invention Organic compounds containing hydrogen atoms are in particular those which a) have a boiling point at least 200C above the cleavage temperature, b) in the temperature range from -20 to 1000C with carbamic acid chlorides with elimination of hydrogen chloride react to form isocyanate addition compounds and c) their addition compounds with aliphatic monoisocyanates of the above formula R-NCO in the temperature range split off the corresponding monoisocyanate from 1000C to 2500C, these requirements correspond in particular to those which are preferably suitable for the method according to the invention Compounds which have at least one grouping of the formula - S02-NHR1, where R1 is an aliphatic or aromatic hydrocarbon radical and preferably denotes a methyl, ethyl, propyl or butyl group. These connections In addition to the groups mentioned, they have no further groups under the reaction conditions of the process according to the invention on reactive groups. Particularly preferred such compounds are N-monosubstituted amides of sulfuric acid or of organic mono- or polysulfonic acids of the formulas S02 (NHR1) 2 'R2SO2NHR1, R3 (S02NHR1) 2 In these last-mentioned formulas, R has the meaning already given above, while 1 R2 for an aliphatic hydrocarbon radical with 1-20 preferably -1-4 carbon atoms, represents a phenyl or p-toluyl radical and R3 represents a phenylene or alkylene radical with 1-3 carbon atoms.

Typical representatives of these particularly preferred compounds are e.g. N, N'-dimethylsulphuric acid diamide, N, N1-dibutylsulphuric acid diamide, N-ethylethanesulphonic acid amide , N-methyl-benzenesulfonic acid amide, N-butylnaphthalenesulfonic acid amide, N, N'-diethylbenzene-1 , 4-disulfonic acid diamide or N, N'-dipropylpropane-1,3-disulfonic acid diamide.

The at least one suitable for the process according to the invention Grouping of the formula -S02-NHR1 containing compounds can in principle from the corresponding acid chlorides, i.e. sulfuryl chloride or the chlorides of organic Sulphonic acids and primary amines are produced with elimination of hydrogen chloride.

For the process according to the invention, there are preferred in addition to those mentioned or particularly preferred compounds also reaction products of sulfuryl chloride or organic sulfonic acid chlorides with primary diamines or polyamines into consideration. Aids suitable for the process according to the invention are used for the preparation For example, the following sulfonic acid chlorides are suitable: Aliphatic sulfonic acid chlorides with 1 to 20 carbon atoms such as methanesulfonic acid chloride, etiiansulfonic acid chloride, Butanesulphonic acid chloride, octadecanesulphonic acid chloride, methanedisulphonic acid chloride or technical mixtures of different sulfonic acid chlorides, such as those used in sulfochlorination of aliphatic hydrocarbons occur (Ullmann, Vol. 16, p. 562).

There are also aromatic sulfonic acid chlorides of benzene and toluene and of naphthalene with 1 to 4 -SO2-Cl groups are used. As examples are called: benzenesulfonic acid chloride, p-toluenesulfonic acid chloride, benzylsulfonic acid chloride, Benzene-1,3-disulfonic acid dichloride etc.

Examples of primary amines are: methylamine, ethylamine, n-propylamine, iso-propylamine, butylamine, ethylenediamine, propylenediamine-1,2, propylenediamine-1,3. 1,4-diaminobutane, 1,6-diaminohexane, cyclohexylamine, aniline, substituents inert on the core comprising anilines.

The process according to the invention is generally carried out as follows: In the temperature range from -20 to + 1000C the implementation of the at least one takes place active hydrogen atom containing compound with the carbamic acid chloride below Elimination of hydrogen chloride in the presence of the solvents exemplified above.

For this purpose, the reactants are preferably at room temperature mixed, the proportions being chosen so that per carbamic acid chloride group at least one active hydrogen atom of the auxiliary, preferably 1-1.5 hydrogen atoms of the aid are available. After mixing the starting materials, the reaction, i.e. the formation of adducts with elimination of hydrogen chloride by mild Heating within the temperature range mentioned, preferably to 60 to 80 ° C set in motion. After at least 90% of the theoretically expected amount of hydrogen chloride split off and escaped the reaction vessel, the second stage of the reaction according to the invention, the thermal cleavage of the addition product obtained. For this purpose, it is sufficient to bring the reaction vessel to a temperature within the temperature range from 100-2500C, preferably to 130-160 ° C. The monoisocyanate formed distils off immediately after its formation. Depending on the boiling point of the solvent used here are optionally mixtures of monoisocyanate and the solvent used received as a distillate, the purpose further separation must be subjected to a further distillation. Using of low-boiling solvents, these distill before they reach the Decomposition temperature of the adduct while using high-boiling solvents these remain in the reaction vessel.

In general, the majority of the isocyanate is formed at a cleavage temperature from 130 to 1600C. The bottom temperature is used to complete the cleavage to 160-2500C, preferably about 2000C.

After the isocyanate has been separated off, the auxiliary used is in the Swamp unchanged before. By adding more carbamic acid chloride solution the process can be repeated several times. If this is intended, it is expedient to lead the cleavage does not end completely in each case to avoid unnecessary temperature stress to avoid the reaction components.

From the above it is already apparent that the inventive Process is very suitable for continuous implementation. For this will be several reaction vessels connected in series, for example in the form of a cascade. Carbamic acid chloride solution and auxiliaries are continuously mixed and fed to the first reaction vessel, in which at around 500C to 700C the main part of the Hydrogen chloride is split off. In the second reaction vessel, the hydrogen chloride is split off at 700C to 1000C completed. In the third and possibly further reaction vessels, the Isocyanate released and distilled off together with the solvent. From the The bottom of the last reaction vessel is the aid to the starting point of the Process. From the distillate or the combined distillates becomes the isocyanate is isolated by fractionation, the solvent, which still contains carbamic acid chloride may contain, enriched elsewhere with carbamic acid chloride and the Process fed back.

The aliphatic which can be prepared by the process according to the invention Monoisocyanates are valuable starting compounds for plant protection products and Pharmaceuticals.

Example 1 In a 41 four-necked flask with stirrer, contact thermometer and packed column (height = 30 cm, diameter = 5 cm) with a reflux divider at 200C to 1026 g (6 mol) of benzenesulfonic acid methylamide, a solution of 467.5 g (5 mol) of N-methylcarbamic acid chloride in 500 ml of chlorobenzene - given. In the course from 1 hour the temperature is increased to 1000C, with 98% of the calculated amount Hydrogen chloride through the column and the attached reflux divider with the reflux divider closed The reflux condenser will escape and be absorbed in water.

The mixture is then brought to the reflux temperature of the chlorobenzene (1300C) heated. The methyl isocyanate is split off at this temperature a, which can be done for a further 3 hours by gradually increasing the sump temperature to 0 200 C and with the reflux divider open, escapes together with the chlorobenzene. A mixture of 276 g (4.84 mol) of methyl isocyanate and 5 g of N-methylcarbamic acid chloride distills and 540 g of chlorobenzene. (Crude yield 97%). When redistilling this mixture 270 g (4.74 mol) of pure, chlorine-free methyl isocyanate are obtained (pure yield 94.7%).

Example 2 In the apparatus described in Example 1, 654 g (6 mol) methanesulfonic acid methylamide with 467.5 g (5 mol) N-methylcarbamic acid chloride mixed in 500 ml of chlorobenzene at 200C. By gradually increasing the temperature 1000C become 97% of the calculated amount of hydrogen chloride within 90 minutes cleaved.

It is then gradually heated to 1300C.

At this temperature, methyl isocyanate begins - together with the solvent to distill off.

Distill between 130 ° C while gradually increasing the temperature and 2000C within 4 hours together with the solvent 270.8 g of methyl isocyanate (- corresponding to 95% of theory). The purity after redistillation is 267.9 g of methyl isocyanate (corresponding to 94% of theory).

Example 3 Analogously to Example 1, 620 g (5 mol) of N, N'-dimethylsulfurylamide are obtained reacted with 537.5 g (5 mol) of N-ethylcarbamic acid chloride in 500 ml of o-dichlorobenzene.

There are after cleavage of the adduct and redistillation of the isocyanate-solvent mixture 319.5 g of ethyl isocyanate (corresponding to 90% of theory) were obtained.

Example 4 Analogously to Example 1, 738 g (6 mol) of methanesulphonic acid ethylamide are obtained reacted with 607.5 g (5 mol) of N-isopropylcarbamic acid chloride in 500 ml of chlorobenzene.

The pure yield of isopropyl isocyanate is 98% of theory.

Example 5 Analogously to Example 1, 1110 g (6 mol) of p-toluenesulfonic acid methylamide are obtained reacted with 607.5 g (5 mol) of N-propylcarbamic acid chloride in 500 ml of xylene.

The pure yield of n-propyl isocyanate is 96% of theory.

Example 6 In the apparatus described in Example 1, 1282.5 g (7.5 mol) of benzenesulfonic acid methylamide with 467.5 g (5 mol) of N-methylcarbamic acid chloride implemented in 500 ml of chlorobenzene up to 1000C. Then, within 30 minutes the temperature increased to 1600C and held at this level for a further 3 hours. While During this time, 300 ml of chlorobenzene are gradually added dropwise. It distills in Isocyanate-solvent mixture, the 3.5 mol of methyl isocyanate (corresponding to 70 % of theory). After the sump has cooled, 327.3 g (3.5 mol) of N-methylcarbamic acid chloride are obtained added in the form of 50% chlorobenzene solution and, as described, in methyl isocyanate convicted. The process is repeated four more times, each time the the amount of N-methylcarbamic acid chloride equivalent to the methyl isocyanate obtained is replaced will.

The results are shown in the following table: Passage use of methyl isocyanate in Mole of carbamide distillate (in moles) acid chloride 1 5 3.5 2 3.5 3.4 3 3.4 3.6 4 3.6 3.3 5 3.3 3.4 6 3.4 3.2 A total of 2075.7 g (22.2 mol) of N-methylcarbamic acid chloride are used. When the combined distillates are redistilled, 1145.7 g (20.1 mol) of methyl isocyanate (corresponding to 90.5% of theory) are obtained.

Claims (2)

Process for the preparation of monoisocyanates of the Formula R-NCO, in which R represents an optionally olefinically unsaturated aliphatic Hydrocarbon radical with 1-4 carbon atoms, from the corresponding carbamic acid chlorides of the formula R-NH-CO-Cl. characterized in that the carbamic acid chlorides in the presence of solvents which are inert under the reaction conditions with at least one active one Compounds containing hydrogen atoms with elimination of hydrogen chloride to form addition compounds the isocyanate R-NCO converts and the addition compound then thermally into the desired isocyanate R-NCO and the at least one active hydrogen atom having compound decomposed, at the same time the monoisocyanate formed by distillation of the compound having at least one active hydrogen atom separates. 2. The method according to claim 1, characterized in that as at least compounds containing an active hydrogen atom have the characteristic grouping - SO2 -NHR1 containing amides of sulfuric acid or organic sulfonic acids are used where R1 is an aliphatic hydrocarbon radical.