CA1113106A - Process and apparatus for producing substituted thiocarbamates - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE:
Substituted thiocarbamates are produced by contin-uously feeding together a secondary amine and sulphur in stoi-chiometric propertions and in a suitable solvent into a reaction colum subjected to pressure by carbon monoxide. A continuous circulation of the reaction solution is maintained in the co-lumn, and the effluent is subjected to alkylation, the substi-tuted carbamate being derived therefrom continuously.

Description

~131~6 The present invention relates to an improved process for producing substituted thiocarbamates in a continuous cycle.
It is known from the literature that it is possible to synthesize thiocarbamates by reacting a secondary amine with carbon monoxide and sulphur in a suitable solvent and thereafter subjecting the product obtained to alkylation.
The reactions are as follows:

(1~ 2 ~ ~ + CO + 5~ 2 . ~ Rl (+) Rl ! Rl ~ ¦ (+)

(2) ~ N-~j-S J H2 + 113X~ N-C--S R¦ NH X ( wherein: Rl, R2may be the same or different, consisting of alkyl, cycloaklyl or aralkyl radicals, or may form together a bivalent polymethylene radical.
R3 = an alkyl, cycloalkyl or aralkyl radical.
X = a substitutable group consisting of halide, sulphate or sulphonate.
In essence, it happens that in reaction (1) the sec-ondary amine reacts with the carbon monoxide and sulphur to give rise to a substituted ammonium salt of thiocarbamic acid, after -which in reaction (2) this salt reacts with an alkylating agent, forming the substituted thiocarbamate.
Deep study of the mechanism by which the aforesaid known reactionsoccur and a long series of experiments have now enabled the Applicants to develop an improved process and ap-paratus for producing substituted thiocarbamates.

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In effect, heretofore the first of the above-mentioned reactions has always been conducted in the presence of an excess of sulphur by mixing equal molar amounts of secondary amine and sulphur in the presence of carbon monoxide.
Moreover, the two reactions have always been carried out separately and each in a discontinuous manner.
The present invention therefore proposes an improved process for producing substituted thiocarbamates wherein a secondary amine and sulphur in stoichiometric proportions (1 mole of amine ~ 0.5 mole of sulphur) are continuously fed together in a suitable solvent into a reaction column sub-jected to pressure by carbon monoxide while maintaining con-tinuous circulation of the reaction solution in the column, and the effluent from the colums is continuously subjected to alkylation to continously produce the desired thiocarbomates.
The invention also proposes an apparatus for carrying out this improved method,which comprises a column provided downstream with an alkyla~ion reaction vessel from which the desired substituted thiocarbamates are withdrawn continuous In addition to the reaction column - which is prefer-ably a column filled with Raschig rings - and the alkylation reaction vessel, the apparatus according to the invention also comprises a circulating pump for the liquid reactants and control means for the temperature.
The reacted solution is withdrawn from the alkylation reaction vessel in an amount equal (by weight) to that of the supplied reactants.
If it is desired to carry out the continuous process according to the invention with amine and sulphur in stoichiome-tric proportion to each other, it is essential that the sulphur be completely dissolved in the reaction mass which is introduced into the reaction column; in fact, proceeding differently and ~- _ 3 -supplying a sl-urry must be excluded because of the technol-ogical difficulties which would arise in this case in the feed and in achieving the condition of stoichiometric proportions.
According to the invention, the dissolution of the sulphur is effected either by the amine itself, for example as in the event of hexamethyleneimine being employed, or by means of the addition of a certain amount of solution already reacted in the column, when the amine does not succeed in dissolving sulphur in the amount specified by the stoichio-metry of the reaction, for example as when di-N-propylamine or ethylcyclohexylamine is used.
In the second case, use is made of the property of the solution of the thiocarbamic acid salt, obtained by the first reaction of the process, of dissolving the sulphur. In this regard, it is provided that the product which is formed be utilized for solubilizing the sulphur, that is one of the substances to be reacted. This obviously considerably extends the number and types of amines which can be used for conducting the said process efficiently.
The carbon monoxide is restored within the column as it is consumed. The amount of carbon monoxide in circulation is very small because of the smallness of the free volume in the reaction column. As a consequence, the process and appara-tus according to the invention have not only the normal advant-ages of a continuous process ~high potentiality, small use of labour, etc.), but also an extreme degree of safety.
The invention will now be described in greater detail with reference to the accompanying drawing, which illustrates diagrammatically an embodiment of the apparatus according to the invention, and with the aid of the examples that follow.
The apparatus shown in the drawing provides two mixing reservoirs SAl and SA2 which are connected alternately . ~

by means of a pump Pl to a conduit CO leading to the top of a reaction column C filled with Raschig rings RA. A reserv-oir Bl containing carbon monoxide under pressure is also con-nected to this column, The reaction colum C has at the bottom a collecting tank SC from the bottom of which there emerges a delivery con-duit CE which bifurcates, being connected on one side to, I ~

the conduit C0 upstream of a circulating pump P2 and on the other side to a heat exchanger F1. The top of the column C
has a gas conduit CG leading to ve~ing means SR2, SR3. The conduit C0 is equipped in large part with a heating jacket R.
The exchanger F1 (the purpose of which is to cool the solution issuing from the collecting tank SC in order to ¦avoid decomposition of the product during transition to ¦ambient pressure) is connected to an alkylation reaction ¦vessel SA3 equipped with a stirrer and an overflow TP from ¦which a pipe TS leads to a storage tank SR1.

Example 1 S-ethyl-N,N-hexamethylene thiocarbamate is prepared by the following reactions: 5-) (+) CH2-CH2-CH2 !CH2-CH2-CH2 ~ ~CH2 CH2 -CH2--(1) 2 ¦ NH+CO+S -~ ¦ N-C-S~ H2N l CH2-CH2-CH2 , CH2-CH2 CH2 / H2-CH2 -CH

¦ /CH2-CH2-CH2 \ (-) CH2-CH2-CH2 ~+) 1(2~ -C-S~ H2 N/ l + ~C2H5)2 S04 -;

¦ ~CH2-CH2-CH2 0 CH2-CH2-CH2 ¦ CH2-CH2-CH2 CH2-CH2-CH2 (~ ) N-C-S-C2H5 + ~ ~H2 S04C2H5 CH2-CH2-cH2 0 CH2 CH2 H2 ¦ The reactants are introduced into a mixing reservoir, SA
or SA2 alternately, with a capacity of 10 litres, in the ¦following proportions:
¦ Hexamethyleneimine 99% 1000g (10 moles) ¦ Sulphur 160g ( 5 moles) ¦Vigorous stirring is carried out until complete solubilizatio 1,....

of the sulphur is obtained and then there is introduced:
Anhydrous toluene 2600g Stirring is maintained throughout the time of the feed.
Into the reaction column C, having a diameter of 5 cm and a height of 400 cm and being filled with Raschi~ rings and maintained at a temperature of 95~- 105C by heating with a jacket and under a carbon monoxide pressure of 8-10 atm., there is delivered by means of the pump P1 the amount of mixture required to fill the collecting tank SC up to the level LI. The pump P2 is turned on so as to create a circulat on in the column: the delivery of the pump is adjusted at a valu between 60 and 200 l/h.
The mixture is left to circulate at a temperature of 95-105C for 30-60 minutes and then the feed of the column by means of the pump P1 is resumed at a rate of 15-20 kg of mixture per hour.
At the same time, there is tapped off from the collectin tank SC an amount of reacted product equal to the fed amount maintaining the level LI constant.
The carbon mon`oxide is supplied at the top and bottom of the column and is consumed in a practically theoretical amount; however, to avoid a concentration of gaseous impuri-ties in the column, a certain amount of gas (1 or 2 bubbles er second) is elimlnated through the venting means SR2 and R3. The temperature ln the column C is preferably maintained t 95-105C, making Use of heatlng applied in a jacket R
o the circulatlon condult C0, ina~much a~ at lower tempera-ures the reaction is slower, while at higher temperatures it s possible to have decomposition of the product obtained.
The pressure in the column is preferably maintained at 8 - 10 atm., which is sufficient for good progress of the eaction. The quantity of product tapped off is cooled to I
30-40~C in the e~changer F1 (it is necessary not to ~o below ¦this temperature so as not to produce crystallization of the ¦salt) and is delivered to the 10-litre ethylation reaction ~essel SA3.
¦ Simultaneously, diethyl sulphate is fed into the reactio ~essel SA3 (3.1 4.1 kg/h ) ¦ The temperature in the ethylation reaction vessel SA3 is ~aintained at 35-40C. Fitted in the reaction vessel is a ~ateral outlet (calculated so as to achieve a permanence time ~f about 30 minutes in the reaction vessel) from which the ~eacted mass issues by overflowing and is sent to the storage tank SR1. By this process there is obtained a toluene solutio ~f ¦ S-ethyl-N,N-hexamethylene thiocarbamate at about 23%.
~he total yield is higher than 90% of the theoretical.
~xample 2 ¦ S-ethyl dipropylthiocarbamate is prepared by the follow ~ng reactions:
¦ CH3-CH2-CH2 . ¦CH3-CH2-CH2 ~~) CH2-CH2-CH3 ~) ~ NH+CO+S-->I N-C-S) H2 N\

CH3-CH2-CH2 ~CH3-CH2-CH2 0/ CH2-CH2-CH3 'H3-CH2-CH2 (-)~CH2-CH2-CH3 ¦~) N-C-S H2 N\ ~ 2 5)2 4 >

3 H2 CH2 0 CH2-CH2-CH3 I CH3 CH2 CH2\ CH3-CH2-CH~ (+) (-) > N~C-S-C2H5 + ~ NH2 SO4 C2 H5 ¦ 3 2 2 CH3-Ch2-CH2 ¦ The same apparatus as is described in Example 1 is used.

The reactants are introduced into a mixing reservoir, SA1 or SA2 alternately, with a capacity of 10 litres, in the following proportions:
- solution of the dipropylammonium salt of dipropyl-thiocarbamic acid at about 23~ (in toluene): 3000 ml - di-N-propylamine at 98% 678 ml - sulphur 84 g Stirring is carried out until complete solubilization of the sulphur is obtained (it should be noted that the sulphur cann~ t dissolve in the di-N-propylamine alone, for which reason it is necessary to recycle the thiocarbamic acid salt) and then there is introduced Toluene 1500 ml.
The amount of solution of the thiocarbamic acid salt introduced is not critical and is adjusted so as to obtain complete solubilization of the sulphur.
The operating conditions are as follows:
-~ Column temperature 80-85~C
Tapping-off temperature 35-40C
C0 pressure in column 8-10 a~m.
;~ Delivery of recycling pump (P2) 80-200 l/h.
Delivery of metering pump (P1) about 13 l/h.
The ethylatlon of the solution containing the salt obtai _ d ln the c~lumn C is carried out, as in Example 1, in the eaction vessel or tan'~ SA3, supplying dlethyl sulphate at a ate of about 860 ml/h. By thls process there is obtained a oluene solution of S-ethyl dipropylthiocarbamate at about 23%.
he total yield is higher than 85% of the theoretical. The ield can be increased to values higher than 95~ if at the ~ottom of reaction column there is connected a second, Il I

finishing, column similar to the first.
NOTE
Preparation of S-propyl dipropylthiocarbamate is possibl by this second method by the following reaction:

~CH3-CH2-CH2 \(-) CH2-CH2-CH3 (+) ~ -C-S¦ H2 N\ + CH3-CH2-CH2 I --3 CH3-CH2-cH2 ~ CH2-CH2-CH3 CH3 2 2\ CH3-CH2-CH2 ~~ N-C-S-CH2-CH2- CH3 + \ NH.H I

CH -CH -CH

The alkylating agent is different: propyl iodide is fed into the alkylation re~ction vessel.
~` The yield is higher than 85~.

. Example 3 ::
:~ S-ethyl cyclohexylethylthiocarbamate is prepared by the following reactions:
(1) CH2-CH
2 CH2 '` HC - Nl H + C O + S --->

'~`''', . ~.~` : ` ~ . :~
CH -CH O \~-) CH2-CH (+) ->¦ H~ HC-N-C-S ~ H2 N ~ CH CH2 CH2-CH2 CH2 CH3~ CH2-CH3 CH2 ,CH2 .
CH2-CH2 0 -) CH2-CH2 ( + ?
~2) CH2 / 7 H 7 - CH /CH2 ~

~ ,~ ' \CH2-CH~ CH2-CH CH2-CH3 CH2 CH2 _ :~ - 10 -'~:

' + (c2H5)2 S04 t C~2 HC-N-C-S-C2H5 t-2 2 \ ( ) + C~ HC - NH2 S04 C2 H5 CH -CH CH -CH

The same apparatus as is described in Example 1 is used.
The reactants are introduced into a mixing reservoir, SA1 or SA2 alternately, with a capacity of 10 litres, in the following proportions:
Solution of the ethylcylohexylammonium salt of ethylcyclohexylthiocarbamic acid at about 23~ 2000 g Ethylcyclohexylamine 97% 640 g Sulphur 80 g Vigorous stirring is carried out until complete solubilizatio of the sulphur in the salt and the amine is obtained and then there is added Anhydrous toluene 1500 ml The operating conditions are as follows:
Temperature oE cc)lul;,n (C) R0-100C
Tapping-off temperature 30-40C
C0 pressure in column 8-10 atm.
Dellvery of recycling pump (P2) 80-200 l/h.
Delivery of metering pump (P1)10-15 l/h.
The ethylation cf the salt obtained in the column is carried out ln a continuous manner as ln Exampl~ 1 and 2, supplying diethyl sulphate at a rate of 760-1140 ml/h. ~y this process there is obtained a toluene solution of S-ethyl cyclohexylethylthiocarbamate at about 23%.
The total yield is higher than 85%.

To increase the yield, it is necessary, as in Example 2, to connect at the bottom of the column a second, finishing, column similar to the first.

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Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are difined as follows :

1. In a process for producing substituted thiocarba-mates wherein a secondary amine is reacted with sulphur and carbon monoxide in a suitable solvent and the reaction product is thereafter subjected to alkylation, the improvement comprising:
a) continuously feeding together the secondary amire and the sulphur instoichiometric propertions (1 : 0.5) in the solvent into a reaction column subjected to pressure by the carbon monoxide ;
b) maintaining continuous circulation of the reaction solution in the column ; and c) continuously subjecting the effluent from the column to alkylation, whereby the substituted thiocarbamate is thus obtained continuously.

2. The improved process of claim 1, wherein the sulphur is completely dissolved in the amine and both are fed into the reaction column together with the solvent.

3. The improved process of claim 1, wherein the sulphur is dissolved in a mixture of the amine and the solution of the thiocarbamic acid salt flowing from the column and recycled.

4. An apparatus for carrying out the improved process as in claim 1, comprising a pair of mixing reservoirs, a reac-tion column filled with Raschig rings, a collecting tank at the bottom of the reaction column, a conduit for externally connecting the collecting tank to the top of the column, a cir-culating pump being connected in the said conduit and the said conduit being fed by the said mixing reservoirs by means of a second pump, and a pipe which branches from the said conduit to connect the bottom of the collecting tank to an alkylation reaction vessel via a heat exchanger, the alkylation reaction vessel comprising a stirrer and an overflow, the latter being connected to a storage tank.

5. The apparatus of claim 4, wherein the said external ciculation conduit is provided with a heating jacket over at least part of its length.