CS196173B1 - Method of producing allylisothiocyanate - Google Patents

Description

The present invention relates to a process for the production of allyl isothiocyanate from α-11-chloride and an inorganic thiocyanate such as potassium or sodium, which is used in a wide variety of fields of chemistry as a basic raw material for further syntheses and for agricultural, soil management, food processing and the like.

The known method for preparing organic isothiocyanates is based on the reaction between an alkyl halide and an inorganic thiocyanate, for example sodium, potassium or silver, in an environment of low-boiling alcohols, low ketones, fatty acid esters, for example formic or acetic acid.

From an industrial point of view, the most advantageous method of preparing the reaction between an alkyl halide and sodium or potassium thiocyanate seems to be the most advantageous. In this reaction, the corresponding alkylthiocyanate is formed, which is in equilibrium under given temperature conditions with the alkylisothiocyanate that forms, by a rearrangement from the thiocyanate. For mixtures containing high piocerito iso thiocyanate reaction product is to be heated to about 100 ^C ° C and higher. For many derivatives, this condition is already achieved by the distillation of the crude reaction product itself.

As mentioned above, it is known to carry out the reaction between an alkyl chloride and an inorganic thiocyanate in an ethyl alcohol or ester medium. It is also known to prepare the above raw materials in acetone and aqueous media.

The reason for using organic solvents as the reaction medium for isothiocyanate synthesis is due to concerns about hydrolysis of the alkyl chloride to the corresponding alcohol and poor contact of the liquid phases if the reaction medium is water.

The present technological arrangement operating in most cases in industrial solvent production carries the major disadvantage that the precipitated reaction chloride, mostly sodium or potassium, is contaminated by the sorbed isothiocyanate and the solvent used, which makes it a very, difficult industrial waste, for which has not yet been found suitable for large-scale production. This is mainly due to the fact that the isothiocyanates smell unpleasant, the chlorides are soluble and cannot be stored and the entrained unreacted thiocyanate then stains all contaminated objects or the environment with intense red contact with iron (III) ions.

Another procedure that eliminates the shortcomings of the reaction carried out in organic solvents is the reaction between allyl chloride and thiocyanate in an aqueous medium. A further improvement is obtained if a saturated solution of the same cationic chloride as the inorganic thiocyanate used is used instead of the pure aqueous solution.

This avoids the possibility of hydrolysis of the resulting allyl isothiocyanate product to the allyl alcohol and increases the yield of the reaction. The separated salt from the reaction medium no longer contains a large amount of inorganic thiocyanate and, in particular, does not contain an organic solvent which has been unpleasantly disturbed by further processing or treatment. recovery of waste salt.

A disadvantage of this known process is the need to carry out the reaction between allyl chloride and an aqueous solution of inorganic thiocyanate at a relatively low temperature. The reaction device must be provided with a relatively efficient cooling system. The reaction at low temperature necessarily prolongs its time, which prevents a higher conversion and thus increases the production cost per tonne of crude allyl isothiocyanate produced.

These drawbacks of the prior art are overcome by a process for the production of allyl isothiocyanate from allyl chloride and an inorganic thiocyanate, such as potassium or sodium, in an aqueous medium,

The two components are reacted together at a temperature of 100 to 150 ° C in a thiocyanate: allyl chloride molar ratio of 1: 1.15 to 1.5, preferably 1: 1.15, in two steps in which the first allyl chloride to an aqueous solution of inorganic chloride formed by the reaction of allyl chloride and inorganic thioisocyanate from the second step and containing 2 to 10% residual inorganic thiocyanate.

After the reaction between residual inorganic thiocyanate and allyl chloride, the aqueous phase free of inorganic thiocyanate is withdrawn and the organic phase containing the allyl chloride and allyl isothiocyanate formed in the first step is treated in the second step with an aqueous solution of inorganic thiocyanate and then the crude reaction mixture the residual allyl chloride distills off the allyl isothiocyanate by distillation.

The advantage of this procedure is that the reaction takes place in a closed apparatus in homogeneous liquid phases, because the heterogeneous medium causes difficulties in stirring the reaction medium, filtering and phase separation.

A further advantage of the process according to the invention is that the reaction time of the alkylation in aqueous medium is substantially reduced by approximately 10-fold, due to the increased temperature in the individual reaction stages and to the fact that the reaction proceeds in liquid phase always with excess of one of the reactants.

The process according to the invention can be carried out batchwise in batch reactors or by a continuous process.

The process according to the invention is explained in more detail in the following examples.

Example 1

15.0 kg of brine containing a propeller stirrer were introduced into an enameled reaction vessel with a duplicator equipped with a propeller stirrer.

18.2 KaCl and 6.8 wt. sodium thiocyanate, respectively. inorganic phases from the previous reaction step. Added

3.2 kg of allyl chloride, the reaction vessel was sealed and heated to 105 ° C with stirring for 10 minutes. The vapor pressure of the reaction medium reached 0.56 MPa and after a further 20 minutes the reaction was terminated at 106 ° C and 0.53 MPa. After separation of the liquid phases of the reaction mixture, the anor

Claims (1)

A process for the preparation of allyl isothiocyanate from allyl chloride and an inorganic thiocyanate, for example potassium or sodium, in an aqueous medium, characterized in that the two components are reacted together at a temperature of 100 to 150 ° C in a molar ratio of thiocyanate: allyl chloride 1: 1.15 to 1.5, preferably 1: 1.15, in two steps, in which in the first step all allyl chloride is treated with an aqueous solution of inorganic chloride formed by the reaction of allyl chloride and inorganic thioisocyanate from the second step ganic phase, ie. aqueous salt solution containing 23.5 wt. NaCl in addition to 0.016 NaSCN. The remaining organic phase of the reaction medium of the first alkylation step was treated with 16.9 kg of a 30.5Z solution of sodium thiocyanate and after closing the reactor, the contents were heated to 112 ° C with stirring for 10 minutes. The pressure reached 0.33 MPa and during the reaction, which also lasted 20 minutes, the pressure was reduced to 0.185 MPa at 108 ° C. After separation of the liquid phases of the reaction mixture, a brine containing 6.5 wt. NaSCN, which was processed in another manufacturing operation, and the organic phase, respectively. a crude product whose rectification yielded 6.30 kg of the product, in addition to 0.15 kg of the front volatiles. The yield of the product was 99.5 Z, calculated on the NaSCN used and 93 Z on the allyl chloride used. Example 2 It concerned the same production method but was carried out in a continuous manner. The equipment used consisted of a cascade of three stirred reactors with overflows for the first stage of allylation, a reaction mixture separator from the first stage, a cascade of two stirred reactors for the second alkylation stage, and a second stage separation. 840 masses were fed to the first reactor of the first stage reaction cascade. parts per hour of allyl chloride and all the brine was leaving a continuous second stage separator containing an average of 7.5 parts by weight. unreacted sodium thiocyanate. The reactors were operated at a constant pressure of 0.58 MPa and at temperatures of 105 to 115 ° C. The liquid phase of the reaction mixture was continuously separated in the separator, the lower inorganic phase containing on average 25 wt. NaCl and less than 0.02 wt. NaSCN was removed from the manufacturing process and the upper organic phase was fed together with 30Z sodium thiocyanate solution into the first reactor of the second stage. In the second stage of the reaction cascade, the pressure was about 0.25 MPa and the temperature was 110-120 ° C. The dosed amount of sodium thiocyanate solution was on average 2 730 wt. parts / h. After separation of the reaction mixture from the second stage, in addition to the inorganic phase which is returned to the first stage, 1,030 parts by weight are obtained. of the organic phase, i.e. the crude product, whose rectification yielded 1000 parts by weight. 99Z product, next to approx. volatile fractions. Thus, an average of 99.1X yield, calculated on NaSCN and 92.5Z yield based on the allyl chloride in feed, was achieved. Example 3 The same procedure was carried out as in Example 1. However, using potassium thiocyanate instead of sodium yielded higher yields, an average of 99.5 Z calculated on thiocyanate and 95 Z calculated on allyl chloride. And containing 2 to 10% residual inorganic thiocyanate, after reaction between residual inorganic thiocyanate and allyl chloride, the aqueous phase free of inorganic thiocyanate is withdrawn and the organic phase containing allyl chloride and allyl isothiocyanate formed in the first step is treated in the second step of an inorganic thiocyanate, and the allyl isothiocyanate is separated by distillation from the crude reaction mixture containing allyl isothiocyanate and residual allyl chloride.