CA1099280A - Product of a chlorothioformate - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A process is disclosed for the production of a chlorothioformate of the formula in which R is alkyl, lower cycloalkyl-methyl, lower cycloalkyl, lower alkenyl, phenyl, chloro-substituted phenyl, benzyl or chloro-substituted alkyl in which the chloro-substituent is situated at least as far as the gamma-carbon atom with respect to the sulfur atom.
The process is conducted in two stages, both occurring a con-tinuous liquid phase in the presence of an activated carbon catalyst.

Description

~c~ ~d -ld Pri~r ~r~
This invention relates to the produc tion of e thyl chlorothioformate by the reaction o ethyl mercaptan with phosgene in the presence of an activated carbon catalyst, C2H5~ ~ COC12 ~ C2H5SCCl ~ HCl Ethyl chlorothioorma~e is a u~eful intermediate for the production of herbicidally e~ective ~hiocarba~na~es. The reaction between e~hyl mercap~an and phosgene to produce ethyl chlorothioforma~e is described in U~S. Pa~ent 3,1659544 of Harry Tilles5 which discloses the conduc~ of this proces~
in laboratory siæe equipment. It is pointed ou~ that reaction temperatures should be maintained as low as possible, con~
sonant with reasonable reaction rates since at ~igh tempera-tures the alkyl disul~ide by-produc~ begins to for~ in significan~ amounts. Maximum temperature is ~uggested or this reactioQ using ethyl mercaptan at between about 75 and 140C.
One process utilized for production of ethyl chloro-thioformate by ~his reaction emplo~s two ca~alytic bed^~ of activated carbon arra~ged in serie~. The irst bed is pre-ferably contained in tubes of a multi-~ube reactor; the ~econd is in the form of a packed bed reactor containlng a ~ingle catalys~ bed~ The first~reactor is operated as a cont~nuous liquid phase reactor; more specifically a~ an upflow tubular ca~alytic reactor, with starting ma~erials introduced at the bottom and product~ removed from the upper portion. The partially reac~ed mi~ture 1~ then in~roduced : in~o the top o the second reactor) which unctions as a tr~ckle-flow (downflow) packed bed. That ls, th~ ~econd reactor is operated in the continuouæ gas phase since g~eous

- 2 -, 9 ~

~ydrogen chloride produc~ is continuously passing up-wardly through the bed. Reaction products are removed from the lower portion of the second reactor and passed to downstream apparatus for separating e~hyl chlorothio-formate, Operation of this process, however9 has be~n ~ound to produce ethyl chlorothioformate in a purity of only between about 91 and about 95%. The major impurity îs diethyl disulfide~ present in about 3-7~/O~ with m~st of the remaining lmpurities being diethyl dithiocarbonate.
It is an objec~ o the present inVen~iQn to pro-vide an impxoved process for the prod~ction of ethyl chloro~
th~oforma~e by reaction of ethyl mercaptan and phosgene in tha presence of an activated carbon catal~st.
A further objective of the present inven~ion is to prov~de such a process wi~h minimization of diethyl disul~ide by-product.
A third objective of the present invention is to provide such a process with enhanced production capacity, Yet another object o the pre~ent invention is to provide such a process having goo~ temperature control in the reactors.
A still urther objective of the present inve~tion : is to provide ~uch a process having a good conversion of ethyl mercaptan to ethyl chlorothio~ormate.

The present invention compxises a process ~or production of et~yl chlorothioforma~e hy tha reac~ion o ethyl mercaptan with phosg~ in the pre~ence o~ an ac~ivated ~ 3 ~

carbon catalys~ comprising: (a) contacting e~hyl mercaptan with phosgene in a first continuous liquid pha~e reaetion zon~ in ~he presenee of a catalyst comprising ac~iva~ed carbon; (b) removing a first reaction product from the fîr~t reaction zone; ~c) contac~ing the first reaction pro~
duct wlth a catalyst eomprising aetivated carbon in a second continuous liquid phase reaction zone; and (d) r~moving a second reaction product comprising ethyl chloro~h~ofonmate from the æcond reaction zone.

The invention i~ more particularly described with reference to the Figure9 which shows a generalized fl~w sheet for the conduct of the proce~s.
Re~rring to the Figure, ethyl mercaptan in line 1 is combined with phosgene in line 2 and the mI~tu~e intro-duced through line 4 into the lower portion of a first react~r 10. Reactor 10 is opera~ed with reactant~ and pro-duc~s ln a continuous liqu;d phase. Pre~erably, reac~or 10 i9 a ~ubular packed bed reactor containing a plurali~y o tubes filled wi~h ac~ivated carbon of an appropriate particle size such that each ~ube functions in the conventional manner as a miniature packed bed reactor. The reac~ants in stream 4 are introduced into the low~r portion of ~he reactor~
thereby into the lower portions of the lndividual tube~, and pass upwards through the tubas. The average outle~ temperatur~
~5 is generally between a~out 0 and about 70C~ preferably b~tween about 0~ and about 50C. Pre~sures range be~ween about 0 and about 150 psig, pre~erably between about O and abou~ 50 psig.

~ 28 ~

The par~ially xeacted product~ from the first reactor 10 are removed from the upper part of this reactor as overhead in line 6 and passed through line 8 înto a second reactor 11. Reac~or 11 contains a packed bed 12 of activa~ed carbon. The reac~ion is completed in reactox 11 in a con~inuous liqu~ phase. As shown in the Figure 3 this is accomplished by introducing reactants i~to the lower portion of reactor 11 so tha~ this reactor operates in so~called "100~ed upflow" condition. The reactor is generally operated at average outlet temperatures of between about 0 and about 70C~ preferably between about 10 and about 50C, most preferably at a temperature within this range beLow 50C. Pres~ures range between about 0 and about 150 psig, pre~erably between about 0 and about 50 psig.
Residenc time of the reactants in reac~or 11 is generally between about 1 and about 180 minutes 9 preferably between about 5 and about 90 minutes.
The xeaction produc~s are removed from reac tor 11 through overhead line 9, passed to separation drum 13 and product eth~l chloro~hiofonmate is removed i~ lin~
15 for further purification. Gaseous by-products (primarily hydrogen chloride wi~h some unreac~ed phosgene) are ~aken off at line 14 and passed to downstream purification un:Lts (not sho~n) for recovery of unreacted sltarting materials or recycle and removal and further processing of hydrogen chloride.
When, as in the prior process~ ~he second reactor 11 is operated as a continuous gas phase reactor (e.g. as a ~rickle-flow packed bed reac~or) the average ou~let tem-perature can also be maintained at between about 0C and about 70C, as in the present process. However, operation according Z81~

to the prior process results in an uneven tempexature proflle across the reac~or due to poor heat transfer, providing localized high temperature zones, or '~o~
spots". I~ is known, from U S. pate~t 3,l65,5449that un desirably high tempera~ures contribute to the formation of by-product die~hyl disulfide. The presence o~ hot spots in reactor ll, ~herefore, increase~ the possibilityo ~ormation of this by-product.
When the process is prac~iced usi~g ~he present invention, however9 t~ operation of the second reactor 11 as a con~inuous liquid phase packed bed reactor reslllts in a marked decrease in diethyl disulfide ~ormation since such operation provides better hea~ transfer and a more uniform tempera~uxe distribution throughout the catalyst bed.
Operation according to the present invention, wi~h reactor 11 a continuous liquid pha~e reac~or, results in an increase in the residence time in the second reac~ion at the same flow ~ate of ~he previous process,, by a ~ac~or of a~ least about lO. Surprisingly~ operakion at such tong residence t~mes (for exampl~, 45-90 minutes instead of 45 minutes) does not result in increased by-product ormation so long as the temperature is maintained under good contro7.
Alternatively, the flow ra~e of materials can be increas d to permit operation at Lower residence ~mes in this reaotor and increased capacity9 as well as an increased conversion of ethyl mercaptan to the chlorothioformate~ Preferably ~he fLow ra~e can be increased up ~o 2-2 1/2 ~imes ~hat used previously. At increased ~low rates, residence time in the firs~ reactox lO is also decreased The desired temperature control in reactor 11 and în the overall process can be augmented by introduction of o excess liquid phosgene into ~he system~ either as part of the ~eed in line 2 or separa~e~rS into the reac~or 10. Part or all of this excess will vaporize under the normal operating conditions of xeactor 11, the vaporization absorbing heat generated during the reactionO
~s an alternative method o temperature control7 and also to assist in increasing the overall production of ethyl chlorothioformate, a relatively cold recyc~e stream 5, obtained from downstream processing uni~s (no~ shown), and comprising pr~marily unreacted starting ma~erialsy can b~
introduced into the system. Pref~rably~ the recycle stream inline 5 is introduced in~o reactor 11 via lines 7 and 8 and its presence contributes to the maintenance of a desirably low temperat~re in reactox 11, pre-Eerably one below about 50C. Alternatively, recycle stream 5 can be întroduced via lines 3 and ~ in~o the ~irst reactor 10. Most preferably, temperature control is maintained by a combination of utili2ation of excess liquid phosgerle and introdu~ t~on of the recycle stream into reactor 11.
Operation according to ~he invention~ as will be further seen fr~m the example which ~ollows, results in conversion of approximatcly 94~/O of star~ing ethyl mercaptan and produc~ion of a product o~ about 98% puri~y, containing generally less than 1% diethyl disulfideO Additonally, the use o a continuous liquid phase reactor9 through the in-crease in residence time, provides grea~er capaci~y than a similar uni~ operating using a downflow or t~kle flow packed reactor~ in which the re~ldence time is substantially shorter. As an alternative to the "~looded upflow" type --7~

Z8~

of reac~or shown in ~he Figure, r~ac~or 11 can be opera~ed as a continuous liquid phasa reac~or in any o~her manner as may be convenient, for example as a downflow flooded packed bed reactor, The ollowing examples illustrate ~he prac~ice of the present inven~ion.

A two-reactor system is u~ilized as shown in the Figure, having a capacity for production of about 57~000 pounds per day of ethyl chlorothioformate. The first reactor is a tubular upflow reactor, wî~h the tubes packed with acti-vated carbon ca~alys~. The second reactcris a packed b~d reactor containing a bed o carbon catalyst and is opera~ed as an upflow reactor, Into he irst rcactor9 corresponding to reac~or 10 of the Figure, are fed 22.4 l~.-moles/hr. o~ phosgene and 20,4 lb.-moles/hr. of ethyl mercaptan. The reactor is operated a~ an inlet ~emperature o~ about 15-40C, an outlet temperatuxe of about 50-65C9 and an outlet pre~sure of about 30-36 psig. The partially reacted products from the first reactor are fed in~o the lower portion of the second reactor together with a recycle streæm con~aining 10.7 lb.-moles/hr.
phosgene and 4.7 lb.~moles/hr. ethyl chlorothloormate. The second reactor is opera~ed at an inlet temperature of about 18-26C, an outlet temperature of about 33~49C, an outlet pressure of about 24~28 psig, and a residence t~me of about 75 minu~es~
Conversion of ethyl mercaptan to the chlorothio-ormate was 94%. The product was produced in 98% purity, - 8 ~

2~

containing about 0~5-1/o diethyl disul~ide and about 1%
diethyl dithiocarbonate.

Example 2 The same system was utilized as in Example l, but flow rates of materials were increased to provide a capacity of about 114,000 lbs./day of ~thy7 chlorothioforma~e.
The ~low rates o~ feed phosgene and ethyl mercaptan were respectively 44.8 and 40.8 lb.-moles/hr. The recycle flow rate was 21.4 and 9.4 lb~ moles/hr. respec~ively of phosgene and ethyl chlorothioformate. Operating tempera~ures and pressures were su~stantially the same as in Example 1. The resîdence time of materials in the second reactox was re-duced to about 35 minutes. The product e~hyl chloro-thioormate was again obta;ned in 98% purity~ with 94%
conversion of ethyl mercaptan. Diethyl disulfide content of the product was about 0.5-1%; diethyl dithiocarbonate content was about 0.5%0 ,.. ~.. . .

SUPPLEMENTA~Y DISCLOSURE
-In accordance with the teachings of the Principal Disclosure, an improved process is provid~d for producing ethyl chlorothioformat.e by the reaction of ethyl mercaptain with phosgene. The process is carried out intwo stages, both occurring in a continuous phase in the presence of an activated .
carbon catalyst.
Nowl and in accordance with the present teachings, the invention relates to the production of chlorothioformates by thP reaction of a mercaptan with phosgene in th~ presence of an activated carbon catalyst, O
~1 RSH + COC12 RSCCl + HCl In th~s inventionS R is alkyl, lower cycloalkyl-methyl, lower cycloalkyl, lower alkenyl, phenyl, chloro-substituted phenyl, ben-zyl or-chloro~substltuted alkyl--in which the---chloro sub-s-~1-tuent is situated at lesst ~s far ~s the ~ ~gamm~) c~rbon atom,-with respect- to-the sulfur atom. By the term ~'~lkyl~ vr ~chloro-substitùtPd àlkyl" is meant such groups having from 1 to 15, pre-fer~bly from 1 to 10, ~nd most.preferably from 1 to 6,carbon ~toms, for example, methyl, ethyl, n-propyl, isopropyl 7 n-butyl, seo butyl, isobytyl, n-pentyl, neopentyl, n-hexyl, neohe~yl, n-heptyl, n-octyl, n-decyl~ n-dodecy~ and n-tetradecyl. By "lower alkenyl't is meant such groups having from 2 to 5 carbon atoms 2nd at least one olefinic bond. By "lower cycloalkyll~ is meant cyclo~liphatic groups having from 3 to 7 carbon ~toms, such 8S cyclopropyl and cyclohexyl~ The term "lower cycloalkyl-meth~1" lncludes group~
hav~ng from 3 to 7 c~rbon ~oms in the cyclo ~lkyl portion, ~uch 8~ cyclopropylmethyl=~n~ cyclopentylmeth~l. The term "chloro-ph~nyl" lnclude~ both mono- ~nd polychlorin~ted ph~ngl rlng~
whl~h the chlorine ~tom or atom~ m~y be ~riously substituted.

~ " ,, . .

32~30 In a preferred embodiment of this process, R is alkyl, lower-cycloalkyl, lower cycloalkyl-methyl, ~enzyl, phenyl or chloro-substituted phenyl. Preferred embodiments for the variou~
possibilities for R are: for alkyl- sueh groups having from 1 to 6 carbon atoms 9 particularly ethyl, n-propyl-,~lsopropyl, n~-butyl, sec.-butyl 9 n-pentyl and neopentyl; ~or lower cycloalkyl-cyclobutyl; for lower cyeloalkyl~met~yl-cyclopropylmet~yl and cyclopentylmethyl; for lower alkenyl- allyl; for chloro-substituted-phenyl~,p-chlorophenyl9 or ~he haloalkyls- 3-chloropropyl~
Such chlorothioformates ~re useful intermediates for the production of herbicidally efec~ive thiocarbantates and similar compounds. This reaction between mercapt~ns and phosgene to pro-duce chlorothioorm~tes is described ln U.S. patent 3,165~544 of Harry Tilles, which discloses the conduc~ of this process in laboratory size equipment~ It is pointed out that reaetion tem-peratures should be m~int~ined--as-low-~s~possible, consonant with reasonable reaction--rates-since ~t high ~emperature~ ~ disulfide by-product b~gins to form in significan~ amounts. Maxlmum tem-peratures are sugges~ed fox this reaction of be~ween sbout 70 and 140C.
One process which has been utilized for co~mercial scsle production of lower ~lkyl chlorothioformstes by this reac~on employs two cat~lytic beds of ~ctiv~ted carbon ~rr~n~ed in series.
The f~rst bed is preferably contained in tubes of a mNlti-tu~e reactor; the second ~s in the form of ~ pa~ked bed reactor conW
taining a single catalyst bed. The first re~ctor ~s operated as a continuous li~uid phase reaetor; more spec~ficslly as an upflow ~ubular cs~alytic reactor~ with s~r~ing m~terials introduced ~t the bottom snd produc~ removed from the upper portion. The z~ ~

partially reacted mixture is then introduced into the top of the second reactor, which functions as a trickle-flow Sdownflow) packed bed. That is " the second reactor is ope rated iR the Corl-tinuous gas phase since ~aseous hydrogen chloride product is continuously psssing through the bed. Reaction products are re-moved from the lower portion of the second reactor and passed to downstream ~pparatus ~or separating chlorothioformate.
Operation of this process for production of e~hyl chlorothio~or-mate, however, has been ~ound to produce this product ~n a purity of only between about 91 and about 95% . The maj or impurity ~s diethyl disulfide, present in ~bou~ 3-~0 concentration, with most o~ the remaining impurities being diethyl dith~ocarbonat~. When used to produce n-propyl chlorothioformate" the amount of disul-fide by-product ranged from 1.5 ~ 13.r/~ ~nd ~ver~ged ~ust under 5% and the chlorothioformate purity averaged about 93~.
Summaxy o the Invention -The present invention comprises a process for productionof chlorothioformates h~ving the formul~ RS~Cl, in which R is alkyl, ~ower cycloalkyl, lower cycloslkyl-methyl, lower alkenyl, phenyl, ~hloro-substituted phenyl, benzyl or chloro-sub~tituted al~yl in which the chloro substituent is s~tuated at le~s~ ~s a~
far as the gamm~ carbon atom, with respect to the sulfur atom, by the reaction of the corresponding mercaptan with phosgene in the presence of ~n activated carbon c~t~lyst eomprising: (~) con tacting the mercap~an with pho~gene in a firs~ continuous liqu~d phase reaction zone-in the presence of ~ catalyst comprlsing acti-vated carbon; (b) removing a first re~ction product from the first reaction zone; (c) cont~cting the first reaction produet with a catalyst compr~sing ~c~ivated carbon ln ~ second con~inuou~ liquid ph~se re~ctlon zone, ~nd (d) removing ~ second re~ctio~ produck compri~ing ~he chlorothioform~te from the ~econd re~ction zone.

Z8C~

~ gain with reference to the Figure of the dxawing which shows a generalized flow sheet for the conduct of the process, a mercaptan in line 1 is combined with phosgene in line 2 and the mixture introduced through line 4 in~o the lower portion of the reactox 10. The reactor-10 is operated at temperatures and pressures outlined previously and the partially reacted products from the firs~ reac~or 10 are removed from the upper part of this reactor as overhead in line 6 and passed through line 8 into a sec~nd reactor 11. If desired, gaseous products from reactor 10 may be separated from the mixture in line 6 prior to its introduction into reactor 11~ The reactor 11 which contains a packed bed 12 of activated carbon is operated at temperatures and pressures as outlined previously.
Operation according to ~he present invention, with re-actor 11 ~ continuous liquid phsse reactor, results in an i~crease in the residence time in the second-reaetor t the sam~ flow ra~e as the previous process, b~ ~ factor`of at least abou~ 10.
In the previous process, for instance, resldence tlme in th~s reactor was often in t~e order of 4 - 5 minutes. In t~e present process the residence time may be between about 5 and about 180 minutes, or even longer~ according to the flow rate. Preerably, the residence time is between about 45 and about 180 minutes, more preer~bly between about 45 and abou~ 90 or 120 minutes. It could reasonably be expected that oper~tlon 3~ such longer res~dence times could result in i~cre~sed by product form~tlon;
however, ~t w~s ound, surprisingl~ th2t opera~lon ~t such long '. !
residence times does not result in increased by-product form~t1on so long as ~he temper~ture ls maint~ned under good control. A1-terna~ively, the flow r~te of m~terial~ c~n be 1ncreas~d to pex-~it oper~tion ~t low~r re~de~ce tim~ thi~ renctor ~d incre~
ed c~pacity~ a~ well ~ ~n 1ncre~ed conver~ion of mercapt~n to ~ht orothioformate. Preferably the fl~w rate csn 'be increased up to 2-2 1/2 times that used previously. At increased flow rates, residence time in the first reactor lO is also decreased.
The desired temperature con~rol in reactor 11 and ln the overall process can be augmented by introduction of exoess liquid phosgene into the system~ either as p~rt of the fee-d in line 2 or separ~tely, into the reactor 10. Part or all of this excess will vaporize under the normal operat~ng conditions of reactor 11, the vaporizatîon abs~rbing heat generated dur~ng the re~ction.
As an alternative method of temperature control~ and also to assist in incre~sing the overall production of chlorothio~
form~te, a relatively cold recycle stre~m 5, obtained from down~
stream processing units (not shown), ~nd comprising primarily unreacted starting m~ter;als, can be introduced into the systemO
The recy~le stre~m in line 5 can be introduced into reactor 11 via lines-7 and 8; its presence contributes-to the maintenance of a desirably low ~emperature in reactor 11~ preferably one below about 5~C. Alternatively, recycle stream 5 can be introduced via lines 3 and 4 into the f lrst reactor 10 . Most preferably~
tempersture control is maintained by a combination of utilization of exce~s liquid phosgene and introduction of the recycle stream into reactor ll.
Operation according to the invention, as will be fuxther seen from the examples which follow, results in conversion of approximately 94% of starting ethy~ mercaptan and production of ~ product of about 98~ ~urity, containing generally less than 1% dieth71 disulfide. Addltionally~ the use o ~ continuous liquid phase reactor, ~hrough the increa~e in resldence time~
provides gre~ter ~apacity than 3 simil~r unlt operatlng u~i~g ~
downflow or trickle flow p~ked reactor, in which ~he residence z~

time is substantially shorter. Similar results were found in the case of n-propyl chlorothioformate, as can be seen from Ex~mple

3. On the basls of ~hese results and the general knowledge in this art, for example the information contained in U.S. patent 3,165,544, ~t is reasonable to expect similar good performance for the other types of compounds included herein. As ~n alterna-tive to ~he "flooded upflow'l type o~ reactor shown in ~he Fi~ure, reac~or 11 can be operated as a continuous liquid phase reactor in sny other manner as may be convenient, for example as a down~
flow flooded packed bed resctor.
The following additional example fur~her illustrates the practice of the present invention.

A two-reactor system ls utilized as shown in the Figure;
having a ~apacity ~or production of about 74,000 pounds per day of n-propyl chlorothioformate. The first reactGr is a tubul ar upflow reactor, w~th the tube~ pRcked w~th activated carbon catalyst. The second reactor is a packed bed reactor containing a bed of carbon catalyst and is operated as an upflow reactor~ :
Into the flrst reactor, corresponding to reactor 10 o the Flgure, are fed 24,6 lb.-moles/hr. of phosgene and 2204 lb./-moles/hr. of n-propyl mercaptan. A recycle stream containing about 11 lb.-moles/hr. phosgene and about 5 lb./moles1hr. n-propyl chlorothloformate is also introduced into reactor lOo The reactor is operated at ~n inlet temperature of abou~ 15-40C~ n outlet temperature of about 40-55C., and 3n outlet pressure of about 26-30 psig. The parti~ily reacted products from the fir:s~ re~-actor are fed into the lower portion of the seeond reactor. The ~econd reactor is oper~ted ~t an lnlet temperature of about 40-55C~, ~n outl2t temper~ture of about 40-55C., ~n outlet ~ . .

~ 8 ~

pressure.of about 22-26 p~ig, and ~ residence ~ime of about 75 minutes.
Conversion of n-propyl mercaptan to the ehlorothioformate was 94%. The product was produced in 98-99% purity,

Claims (40)

WHAT IS CLAIMED IS:

1. A process for production of ethyl chlorothio-formate comprising:
a) contacting ethyl mercaptan with phosgene in a first continuous liquid phase reaction zone in the presence of a catalyst comprising activated carbon;
b) removing a first reaction product from the first reaction zone;
c) contacting the first reaction product with a catalyst comprising activated carbon in a second continuous liquid phase reaction zone;
and d) removing a second reaction product comprising ethyl chlorothioformate from the second reaction zone.

2. A process according to Claim 1 in which step (c) is operated at an average outlet temperature of between about 0° and about 70°C.

3. A process according to Claim 1 in which step (c) is operated at an average outlet temperature of betwen about 10° and about 50°C.

4. A process according to Claim 1 in which step (c) is operated at an average outlet temperature of between about 10° and below about 50°C.

5. A process according to Claim 1 in which step (c) is operated at a residence time of between about 5 and about 90 minutes.

6 . A process according to Claim 5 in which step (c) is operated at a residence time of between about 45 and about 90 minutes.

7. A process according to Claim 1 in which an excess of liquid phosgene is introduced into step (a).

8. A process according to Claim 1 in which an excess of liquid phosgene is introduced into step (c).

9. A process according to Claim 1 further com-prising recovering unreacted starting materials from the product of step (d) and recycling said unreacted starting materials to step (c).

10. A process according to Claim 1 further com-prising recovering unreacted starting materials from the product of step (d) and recycling said unreacted starting materials to step (a).

11. A process according to Claim 1 further com-prising recovering ethyl chlorothioformate from the products of step (d).

12. A process according to Claim 1 in which step (c) is conducted by introducing the first reaction product into the lower portion of a packed bed reactor containing a bed of activated carbon catalyst.

13. In a process for the production of ethyl chlorothioformate by the reaction of ethyl mercaptan with phosgene in the presence of a catalyst comprising activated carbon in a system comprising two reactors operating in a series, the improvement comprising operating the second reactor as a continuous liquid phase reactor.

14. A process according to Claim 12 in which the second reactor is operated as a flooded upflow packed bed reactor.

CLAIMS SUPPORTED BY THE SUPPLEMENTARY DISCLOSURE

15. A process for production of a chlorothioformate having the formula in which R is alkyl, lower cycloalkyl-methyl, lower cycloalkyl, lower alkenyl, phenyl, chloro-substituted phenyl, benzyl or chloro-substituted alkyl in which the chloro-substituent is situated at least as far as the gamma-carbon atom, with respect to the sulfur atom, comprising:
a) contacting a mercaptan having the formula RSH
with phosgene in a first continuous liquid phase re-action zone in the presence of a catalyst comprising activated carbon;
b) removing a first reaction product from the first reaction zone;
c) contacting the first reaction product with a catalyst comprising activated carbon in a second continuous liquid phase reaction zone; and d) removing a second reaction product comprising the chlorothioformate from the second reaction zone.

16. A process according to Claim 15 in which R is alkyl.

17. A process according to Claim 16 in which R is alkyl having from 1 to 10 carbon atoms.

18. A process according to Claim 16 in which R is alkyl having from 1 to 6 carbon atoms,

19. A process according to Claim 18 in which R is n-propyl.

20. A process according to Claim 15 in which R is lower cycloalkyl.

21. A process according to Claim 20 in which R is cyclo-hexyl.

22. A process according to Claim 15 in which R is benzyl.

23. A process according to Claim 15 in which R is phenyl.

24. A process according to Claim 15 in which R is chloro-substituted phenyl.

25. A process according to Claim 24 in which R is p-chloro-phenyl.

26. A process according to Claim 15 in which step (c) is operated at an average outlet temperature of between about 0°
and about 70°C.

27. A process according to Claim 15 in which step (c) is operated at an average outlet temperature of between about 10°
and about 50°C.

28. A process according to Claim 15 in which step (c) is operated at an average outlet temperature of between about 10°
and below about 50°C.

29. A process according to Claim 15 in which step (c) is operated at a residence time of between about 5 and about 180 minutes.

30. A process according to Claim 29 in which step (c) is operated at a residence time of between about 45 and about 180 minutes.

31. A process according to Claim 15 in which an excess of liquid phosgene is introduced into step (a).

32. A process according to Claim 15 in which an excess of liquid phosgene is introduced into step (c).

33. A process according to Claim 15 further comprising recovering unreacted starting materials from the product of step (d) and recycling said unreacted starting materials to step (c).

34. A process according to Claim 15 further comprising recovering unreacted starting materials from the product of step (d) and recycling said unreacted starting materials to step (a).

35. A process according to Claim 15 further comprising recovering the chlorothioformate from the products of step (d).

36. A process according to Claim 15 in which step (c) is conducted by introducing the first reaction product into the lower portion of a packed bed reactor containing a bed of activated carbon catalyst.

37. A process according to claim 15 wherein the first and second reaction zones comprises reactors operating in a series with the second reactor operating as a continuous liquid phase reactor.

38. A process according to claim 37 in which the second reactor is operated as a flooded upflow packed bed reactor.

39. A process according to claim 37 in which the mercaptan is an alkyl mercaptan and the chlorothioformate is an alkyl chlorothioformate have from 1 to 6 carbon atoms in the alkyl group.

40. A process according to claim 39 in which the alkyl group is n-propyl.