To this is added an equal volume of ethyl alcohol and the reaction mixture is resaturated with the hydrogen sulfide. Finally, a quantity of benzyl chloride dissolved in alcohol is added. The mixture is allowed to stand in the cold, with frequent shaking for 4 days, and kept cold to prevent as much as possible the oxidation of the mercaptan to the disulfide and the formation of the monosulfide, which, it is disclosed, takes place readily at high temperatures.
A conventional process for making benzyl mercaptan, as disclosed in U. STR2 A problem which occurs in this reaction, however, is that significant quantities of benzyl sulfide are produced as a by-product. This reduces the yield of benzyl mercaptan and increases the need for purification of the product which is produced. It would be advantageous, therefore, to find a process for the production of benzyl mercaptan which minimizes the quantity of benzyl sulfide by-product formed during the reaction and optimizes the percent yield of the desired benzyl mercaptan obtained.
This invention is concerned with such a process. The preferred benzyl halide for use in the process of the invention is benzyl chloride. Benzyl bromide can be used, but it is more expensive than benzyl chloride.
The preferred alkali metal hydrosulfide salt is the sodium salt. Other salts which can be used include the potassium salt. The process as described above results in benzyl mercaptan of high purity and yield being obtained. There are three elements in the above-described process which are essential to the practice of this invention. The first has to do with the temperature adjustments carried out during the period of the reaction.
Although conducting the reaction of lower temperatures leads to reduced levels of benzyl sulfide impurity, the reaction time becomes excessive. Under these conditions, the level of unreacted benzyl chloride can be reduced to a ow level without appreciably increasing the benzyl sulfide level. The effects of the reaction temperature on benzyl sulfide by-product content in the benzyl mercaptan product are shown in the Table below, wherein a series of runs are tabulated.
In each of these reactions, the reactants were benzyl chloride and sodium hydrosulfide. Under these conditions, approximately 97 weight percent pure product was obtained upon cooling and phase separation.
Another critical factor in carrying out the process of the invention is to conduct the reaction in the presence of a hydrogen sulfide atmosphere. The hydrogen sulfide atmosphere should be a static hydrogen sulfide atmosphere, which can be maintained by adding a strong acid such as HCl to the reaction solution. This strong acid results in a hydrogen sulfide gas being generated, which is effective in maintaining a hydrogen sulfide atmosphere over the reaction solution.
Higher concentrations of hydrosulfide salt extend the reaction time by a factor of 3 or more. Over the course of the reaction the quantity of hydrosulfide salt will diminish. The criticality of the hydrosulfide salt concentration in the solution is demonstrated in accordance with the following Table, which represents a series of reactions which were conducted at various sodium hydrosulfide concentrations. Run Temp. Time Prod. Other solvents can be added, such as methanol, toluene or glycerol.
In general, an excess of sodium hydrosulfide is used to react with benzyl chloride in the process of the invention. Sodium hydrosulfide can be prepared by adding hydrogen sulfide to a sodium hydroxide solution or can be purchased commercially.
As previously indicated, a strong acid, such as aqueous hydrochloric acid, can be used to produce the hydrogen sulfide atmosphere, by adding the acid to the slightly larger excess of sodium hydrosulfide in solution. Preferably, about 0. The acid can also serve to adjust the pH of the solution to insure that the minimum amount of disodium sulfide is present. An economically more attractive synthetic route is the nucleophilic substitution of the chlorine atom in benzyl chloride by an alkaline sulfhydrate, ammonium sulfhydrate or an amine sulfhydrate.
This reaction, generally carried out in an alcoholic medium, has long been known: C. Marcker, Liebigs Ann. Zinner, Chem. Bittell et al, J. These references are hereby incorporated by reference. According to U.
Indeed, the separation of benzyl chloride by distillation from crude benzyl mercaptan is very difficult. On the other hand, the formation of byproducts benzyl sulphide and incidentally benzyl disulphide , although separable by distillation, is prejudicial to the economics of the process.
Finally, the use of an alcohol solvent, which has to be recycled or destroyed before being discarded, complicates a production plant. Thus, there is a need for a process for producing benzyl mercaptan which provides at the same time substantially total conversion of the benzyl chloride and good selectivity for benzyl mercaptan.
This is without the use of alcohol as the reaction medium. The reaction is carried out under autogenous pressure in a closed reactor in two steps. The concentration of the aqueous solution of ammonium sulfhydrate may vary within wide limits because it has no significant effect on the yield or the conversion. The equation for the reaction is: NH. To promote the complete conversion of the benzyl chloride, it is desirable to use at least a slight excess of ammonium sulfhydrate for example, about 1.
The optimal molar ratio is around 1. During the addition, the temperature may be kept at the selected value. The duration of the addition of benzyl chloride does not appear to have any effect on the results.
This invention is concerned with such a process. An economically more attractive synthetic route is the nucleophilic substitution of the chlorine atom in benzyl chloride by an alkaline sulfhydrate, ammonium sulfhydrate or an amine sulfhydrate. On the other hand, the formation of byproducts benzyl sulphide and incidentally benzyl disulphide , although separable by distillation, is prejudicial to the economics of the process.
The synthesis of benzyl mercaptan by the action of hydrogen sulphide on benzyl alcohol in the presence of a catalyst is not economically viable due to the high price of benzyl alcohol and its undesirable characteristics during catalysis deactivation of catalysts and rapid loss of selectivity. The optimal molar ratio is around 1. The lower organic phase was separated to give, as identified by gas chromatography, Desirably, the pH of the solution should be about 8.
An additional 1. Then hydrogen sulphide is added moles up to the total absorption corresponding to the formation of NH4 SH. The reaction mixture was washed once with 60 ml of warm water and twice with 60 ml of 3N hydrochloric acid solution. During the addition, the temperature may be kept at the selected value.