Note: Descriptions are shown in the official language in which they were submitted.
~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
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,
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
- 5 -
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
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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.
- 12 -
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
- 14 -
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.
EXAMPLE 3
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,
