Process for the preparation of chloroformic acid aryl esters

In a process for the preparation of an aromatic chloroformic acid ester by contacting a phenol and phosgene, the improvement wherein the reaction is carried out in a homogeneous liquid phase at a temperature of 60.degree. to 180.degree. C. in the presence of organic phosphorus compound of the formula EQU R.sup.1 R.sup.2 R.sup.3 PR.sup.4.sub.n X.sub.n in which PA1 R.sup.1, R.sup.2 and R.sup.3 independently of one another represent hydrogen, alkyl, alkenyl, aralkyl, aryl or halogen and two of the said radicals together with the phosphorus atom can form a 5-membered or 6-membered phosphorus-containing saturated or unsaturated heterocyclic radical, PA1 X represents OH, homopolar-bonded halogen or an inorganic or organic acid anion, PA1 R.sup.4 denotes hydrogen or alkyl or, if X denotes halogen, can also denote halogen and n denotes 0 or 1, and in which, furthermore, PA1 R.sup.4 and X together can represent oxygen or sulfur.

The invention relates to a process for the preparation of chloroformic acid 
aryl esters by reacting phenols with phosgene in the presence of organic 
phosphorus compounds. 
The reaction of alcohols or phenols with phosgene to give the corresponding 
chloroformic acid esters has already been disclosed (Ullmanns Enzyklopadie 
der technischen Chemie (Ullmann's Encyclopaedia of Industrial Chemistry), 
4th Edition, Volume 9, page 381, Verlag Chemie, 1975). Whilst aliphatic 
alcohols are able to react with phosgene even without additives, 
additives, for example those which are able to bind the hydrochloric acid 
liberated, must be used when reacting phosgene with phenols. 
Thus, for example, inorganic bases, such as aqueous sodium hydroxide 
solution, can be employed (German Auslegeschrift No. 1,117,598 and British 
No. 1,200,768). These bases must be used in at least the stoichiometric 
amount and this has an adverse effect on the economy of the process and 
give rise to disposal problems since at least stoichiometric amounts of 
inorganic salts are formed. Furthermore, the procedure in the 
water/organic solvent two-phase system impairs the space-time yield of the 
process. 
The addition of organic nitrogen bases has also been disclosed (German 
Auslegeschrift No. 1,213,419 and U.S. Pat. No. 3,211,776). 
However, the use of these bases makes it necessary to carry out the 
reaction in an organic solvent or under elevated pressure in an autoclave. 
This also has an adverse effect on the space-time yield of the process, or 
necessitates the use of apparatus for working under pressure. The 
hydrochloride formed from the amine base added and the hydrogen chloride 
liberated must be removed from the reaction mixture, for example by 
washing the solution, extracting, filtering or decanting, since otherwise 
the hydrochloride formed can block the apparatus during the subsequent 
distillation and results in breakdowns. To avoid these complications, the 
reaction can be carried out in the presence of a resin which contains 
amino groups (U.S. Pat. No. 3,211,775), but in this case also the reaction 
must be carried out under pressure. The additional costs for these 
polymeric catalysts are a burden on the economy of the process. 
Furthermore, working with phosgene and the resulting hydrogen chloride 
under pressure is expensive in respect of corrosion and the maintenance of 
work safety. 
Furthermore, quaternary ammonium salts promote the reaction of phosgene 
with phenols (U.S. Pat. No. 3,255,230). In this case also it is necessary 
to carry out the reaction in a solvent. Good yields are obtained with this 
process using ammonium salts which carry long-chain aliphatic 
substituents, such as stearyltrimethylammonium chloride (Chem. and Ind. 
1965, 791 to 793). These additives are separated off by filtration or 
chromatography and this, like the special additives, results in higher 
costs. 
Furthermore, carboxylic acid amides, such as dimethylformamide, have also 
been recommended as catalytically effective additives (German 
Auslegeschrift No. 2,131,555; U.S. Pat. No. 3,211,774). However, during 
the preparation of chloroformic acid phenyl ester, dimethylformamide and 
phosgene form N,N-dimethylcarbamoyl chloride, which has a highly 
carcinogenic action on mice (C.A. 77, 97 540 b). 
The use of trisubstituted phosphines or phosphine oxides for the 
preparation of hydroxybenzenesulphonic acid halides from the sulphonic 
acid salts on which the latter are based and thionyl chloride, phosphorus 
oxychloride or phosgene has been disclosed in U.S. Pat. No. 3,673,247. 
Furthermore, the use of phosphine chloride compounds and phosphine oxide 
compounds for the preparation of carboxylic acid chlorides from the 
carboxylic acids has been disclosed (German Offenlegungsschrift No. 
2,841,069, German Offenlegungsschrift No. 2,321,122, U.S. Pat. Nos. 
3,544,626 and 4,129,595). 
The reaction of phenols with phosgene in the presence of sodium hydroxide 
solution and in the presence of quaternary phosphorus compounds results in 
the formation of diaryl carbonates (German Offenlegungsschrift No. 
2,804,227 and French No. 1,381,791). 
Furthermore, it is known that aliphatic alcohols react with phosgene to 
form chloroformates if a trialkyl phosphite or PCl.sub.3, which under the 
reaction conditions forms a trialkyl phosphite, is added (Japanese 
Applications Nos. 23409/67 and 7890/67). Aliphatic alcohols can, however, 
also be converted to chloroformates without additives, so that no 
technical advance is discernible by the additions of phosphite or 
PCl.sub.3. Phenol, on the other hand, does not react with phosgene in the 
presence of triethyl phosphite in the temperature ranges of up to 
35.degree. C. indicated in the Japanese Patent Applications, whilst at 
elevated temperature diphenyl carbonate forms. 
A process for the preparation of aromatic chloroformic acid esters from 
phenols and phosgene has now been found which is characterized in that the 
reaction is carried out in a homogeneous liquid phase at a temperature of 
60.degree. to 180.degree. C. in the presence of organic phosphorus 
compounds of the formula 
EQU R.sup.1 R.sup.2 R.sup.3 PR.sup.4.sub.n X.sub.n (I) 
in which 
R.sup.1, R.sup.2 and R.sup.3 independently of one another represent 
hydrogen, alkyl, alkenyl, aralkyl, aryl or halogen and two of the said 
radicals together with the phosphorus atom can form a 5-membered or 
6-membered phosphorus-containing saturated or unsaturated heterocyclic 
radical, 
X represents OH, homopolar-bonded halogen or an inorganic or organic acid 
anion, 
R.sup.4 denotes hydrogen or alkyl or, if X denotes halogen, can also denote 
halogen and 
n denotes 0 or 1, 
and in which, furthermore, 
R.sup.4 and X together can represent oxygen or sulphur. 
An example of alkyl which may be mentioned is a straight-chain, branched or 
cyclic radical with up to 12, preferably 8 and particularly preferentially 
6 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, 
tert.-butyl, pentyl, hexyl, decyl, dodecyl, cyclohexyl or 
4-ethyl-cyclohexyl. Preferred alkyl radicals are butyl or cyclohexyl. 
Examples of alkenyl which may be mentioned are straight-chain, branched or 
cyclic radicals with at least one olefinic double bond and 2 to 12, 
preferably up to 8 and particularly preferentially up to 6 carbon atoms, 
such as 1-propenyl, 2-propenyl, butenyl, 3-methyl-2-butenyl and hexenyl. 
Preferred alkenyl is propenyl or butenyl. 
Radicals which may be mentioned as aralkyl are hydrocarbon radicals which 
have an aliphatic and an aromatic part, such as benzyl, phenylethyl, 
naphthyl-methyl, naphthyl-ethyl and 9-fluorenyl, preferably benzyl. 
Radicals which may be mentioned as aryl are aromatic hydrocarbon radicals 
with up to 15, preferably up to 10 and particularly preferentially up to 7 
carbon atoms, such as phenyl, tolyl, naphthyl, ethylnaphthyl, anthryl, 
methylanthryl, fluorenyl or biphenyl, preferably phenyl or tolyl. 
Examples of halogen which may be mentioned are chlorine and bromine, 
preferably chlorine. 
If two of the radicals R.sup.1 to R.sup.3 together with the phosphorus form 
a 5-membered or 6-membered phosphorus-containing saturated or unsaturated 
heterocyclic radical, examples of such radicals which may be mentioned are 
the phosphol system, the phospholene system, the phospholane system, the 
dibenzophospholane system or the phosphacyclohexane system, preferably the 
phospholene system or the phospholane system. 
In addition to hydroxyl, the substituent X in the formula (I) can also be 
homopolar-bonded halogen, for example chlorine or bromine. The substituent 
X can also be the inorganic or organic acid anion of a phosphonium salt, 
for example chloride, bromide, sulphate, phosphate, methyl-sulphate or 
aliphatic or aromatic sulphonate. 
Furthermore, the radicals R.sup.4 and X together can represent oxygen or 
sulphur, preferably oxygen. 
n denotes 0 or the number 1 and specifically in each case has the same 
meaning for the radical R.sup.4 and for X. 
The organic phosphorus compounds of the formula (I) include, for example, 
phosphines, phosphine oxides, phosphine sulphides, phosphine halides, 
phosphonium salts or halogenophosphines. 
Examples of phosphines which may be mentioned are: tributylphosphine, 
triphenylphosphine, methyldiphenylphosphine, diethylcyclohexylphosphine, 
tricyclohexylphosphine, allyl-butyl-phenylphosphine, 
methylbenzyl-tolylphosphine, 1-methylphosphol, 
1-methyl-2,5-dihydrophosphol, 1-phenyl-2-methyl-2,5-dihydrophosphol and 
1-methyl-dibenzophospholane. Preferred phosphines are tributylphosphine, 
triphenylphosphine and 1-phenyl-2-methyl-2,5-dihydro-phosphol. 
Examples of phosphine oxides which may be mentioned are: 1-methylphosphol 
oxide, 1-phenyl-2-methyl-2,5-dihydrophosphol oxide, tributylphosphine 
oxide, triphenylphosphine oxide and triphenylphosphine oxide hydrate, 
preferably triphenylphosphine oxide. 
An example of a phosphine sulphide which may be mentioned is 
tributylphosphine sulphide. 
Examples of phosphine halides which may be mentioned are triphenylphosphine 
dichloride, triphenylphosphine dibromide, tributylphosphine dichloride and 
tributylphosphine dibromide, preferably triphenylphosphine dichloride and 
tributylphosphine dichloride. 
Examples of phosphonium salts which may be mentioned are 
methyltriphenylphosphonium bromide and methyltriphenylphosphonium 
chloride, tributylphosphonium chloride, tetraethylphosphonium chloride, 
methyltrioctylphosphonium iodide, allyltriphenylphosphonium chloride and 
methyltributylphosphonium methosulphate, preferably 
methyltriphenylphosphonium bromide and methyltriphenylphosphonium 
chloride. 
Examples of halogenophosphines which may be mentioned are 
diphenylchlorophosphine and phenyldichlorophosphine, preferably 
phenyldichlorophosphine. 
Amongst the said compound categories of organic phosphorus compounds, 
alkylphosphines and arylphosphines, alkylphosphine oxides and 
arylphosphine oxides and also the phosphine halides are preferred and the 
phosphines and phosphine oxides are particularly preferred. 
Therefore, the organic phosphorus compounds employed in the process 
according to the invention are preferably those of the formula 
EQU R.sup.5 R.sup.6 R.sup.7 PR.sup.8.sub.n Y.sub.n (II) 
in which 
R.sup.5, R.sup.6 and R.sup.7 independently of one another represent alkyl, 
benzyl, phenyl or chlorine, 
Y represents OH, chlorine or bromine, 
R.sup.8 denotes hydrogen or alkyl or, if X is chlorine or bromine, can also 
denote chlorine or bromine, 
n has the abovementioned meaning, 
and in which, furthermore, 
R.sup.8 and Y together can represent oxygen. 
Organic phosphorus compounds particularly preferentially employed in the 
process according to the invention are those of the formula 
EQU R.sup.9 R.sup.10 R.sup.11 PR.sup.12.sub.n Z.sub.n (III) 
in which 
R.sup.9, R.sup.10 and R.sup.11 independently of one another denote alkyl or 
phenyl, 
R.sup.12 denotes chlorine, 
Z denotes chlorine and 
n has the abovementioned meaning, 
and in which, furthermore, 
R.sup.12 and Z together can represent oxygen. 
Of course, mixtures of the organic phosphorus compounds mentioned can also 
be employed. 
Furthermore, it is possible to use compounds from which the indicated 
organic phosphorus compounds can form under the reaction conditions. For 
the latter case reference may be made, for example, to the reaction of 
trisubstituted phosphines with the hydrogen chloride formed during the 
reaction, to give the corresponding phosphonium salt, and to the reaction 
of phosphine oxides with phosgene to give phosphine halides and carbon 
dioxide. 
Phenols which can be used for the process according to the invention are, 
for example, those of the formula 
EQU R.sup.13 R.sup.14 R.sup.15 Ar.sup.1 (OH).sub.m (IV) 
in which 
R.sup.13, R.sup.14 and R.sup.15 independently of one another represent 
hydrogen, alkyl, halogenoalkyl, aralkyl, aryl, halogen, nitro, cyano, 
alkoxy, alkylthio, aralkoxy, aralkylthio, aryloxy, arylthio, 
alkylthioalkyl, alkoxyalkyl, halogenoalkylalkoxy, trimethylsilyl, 
carboxyl, carboalkoxy, formyl, which is optionally in the form of a 
derivative thereof, alkylamino, which is optionally in the form of a 
derivative thereof, or alkyl-alkinylamino or dialkylamino, 
Ar.sup.1 denotes the benzene nucleus, the naphthalene nucleus, the 
anthracene nucleus, the bis-phenylalkylidene system, the diphenyl oxide 
system, the diphenyl sulphide system, the diphenylsulphone system, the 
diphenylamine system, a heterocyclic aromatic 5-membered or 6-membered 
ring or a benzo-fused heterocyclic ring system and 
m represents a number from 1 to 3, 
and in which 
all of the OH groups except one can be in the form of derivatives thereof. 
Preferably, phenols of the formula 
EQU R.sup.16 R.sup.17 Ar.sup.2 (OH).sub.p (V) 
are employed, in which 
R.sup.16 and R.sup.17 represent hydrogen, alkyl, halogenoalkyl, halogen, 
nitro, cyano or alkoxy, 
Ar.sup.2 denotes the benzene nucleus, the naphthalene nucleus, the 
quinoline ring system, the benzothiophen ring system, the 
benzodihydrofuran ring system, the benzodihydropyran ring system, the 
bisphenyl-alkylidene system or the diphenyl oxide system and 
p represents the number 1 or 2. 
Particularly preferentially, the phenols employed for the process according 
to the invention are those of the formula 
EQU R.sup.18 --C.sub.6 H.sub.4 OH (VI) 
in which R.sup.18 denotes hydrogen, C.sub.1 -C.sub.4 -alkyl, CF.sub.3, 
CCl.sub.3, Cl, Br, NO.sub.2 or C.sub.1 -C.sub.4 -alkoxy. 
With regard to the range of possible meanings for alkyl, aralkyl and aryl, 
reference may be made, for example, to the range of meanings already 
mentioned. 
Radicals which may be mentioned as halogenoalkyl are, for example, 
fluorinated, chlorinated or brominated alkyl radicals with up to 12, 
preferably up to 6 and particularly preferentially up to 4 carbon atoms, 
such as trifluoromethyl, trichloromethyl, tribromomethyl and the 
fluorinated, chlorinated or brominated ethyl, propyl, butyl, hexyl, decyl 
or dodecyl radicals containing various numbers of fluorine, chlorine or 
bromine substituents. 
Halogen substituents which may be mentioned for the phenols which can be 
employed according to the invention are, in addition to chlorine and 
bromine, also fluorine and iodine, preferably fluorine, chlorine or 
bromine and particularly preferentially chlorine or bromine. 
Radicals which may be mentioned as alkoxy are, for example, radicals of 
aliphatic alcohols with up to 12, preferably up to 6 and particularly 
preferentially up to 4 carbon atoms, such as methoxy, ethoxy, propoxy, 
butoxy, hexyloxy, decyloxy or dodecyloxy. 
Radicals which may be mentioned as alkylthio are, for example, the thio 
analogues of the alkoxy radicals mentioned. 
Radicals which may be mentioned as aralkoxy are radicals of araliphatic 
alcohols, such as benzyloxy, phenyl-ethoxy, naphthyl-methoxy and 
naphthyl-ethoxy, preferably benzyloxy. 
Radicals which may be mentioned as aralkylthio are, for example, the thio 
analogues of the aralkoxy radicals mentioned. 
Radicals which may be mentioned as aryloxy are, for example, radicals of 
phenols, such as phenoxy, naphthyloxy and anthryloxy, preferably phenoxy. 
Radicals which may be mentioned as arylthio are, for example, the thio 
analogues of the aryloxy radicals mentioned. 
Radicals which may be mentioned as carboalkoxy are, for example, ester 
groups with up to 4 carbon atoms, such as carbomethoxy, carboethoxy or 
carbopropoxy. 
If the formyl group is in the form of a derivative, examples which may be 
mentioned are the 1,3-dioxolan-2-yl or 4,5-dimethyl-1,3-dioxolan-2-yl 
group. 
Examples of dialkylamino which may be mentioned are dimethylamino, 
diethylamino, dipropylamino, dibutylamino, methylethylamino, 
methylpropylamino or methylbutylamino. In alkyl-alkinyl-amino groups, 
alkyl can be the alkyl radicals mentioned and examples of alkinyl which 
may be mentioned are ethinyl, propinyl or butinyl. 
Alkylamino which may be mentioned is amino substituted by only one of the 
alkyl radicals mentioned. If an amino or alkylamino group is in the form 
of a derivative, examples which may be mentioned are an amide, such as 
acetamide, an imine or amidine or a salt thereof with a hydrogen halide or 
sulphuric acid, or a carbamate group, such as methyl-carbamate or 
ethyl-carbamate. 
If Ar.sup.1 represents the bisphenylalkylidene system, an alkylidene group 
which may be mentioned is a radical with up to 8 carbon atoms, such as the 
methylene group, the 1,1-ethylidene group, the 1,2-ethylene group, the 
2,2-propylidene group, the 1,1,3-trimethyltrimethylene group or the 
cyclohexylidene group, preferably the methylene group, the 1,1-ethylidene 
group or the 2,2-propylidene group. Examples which may be mentioned of a 
heterocyclic aromatic 5-membered or 6-membered ring or of a benzo-fused 
heterocyclic ring system are pyrrole, furan, thiophen, pyridine, 
quinoline, isoquinoline, indole, coumarone, thionaphthene, acridine and 
benzopyran. 
m denotes one of the numbers 1, 2 or 3; p denotes 1 or 2. 
If Ar.sup.1 represents a polynuclear aromatic ring system, the radicals 
R.sup.13 to R.sup.17 and the hydroxyl groups, which are up to 3 in number, 
can be uniformly or differently distributed between the various nuclei of 
such a ring system in the formulae (IV) and (V). 
The OH groups can all except for one also be in the form of derivatives, 
for example derivatives obtained by esterification, thus using acetic acid 
or phosphoric acid, or can be in the form of a mixed alkyl acetal, for 
example of chloroacetaldehyde, or, in the case of two adjacent OH groups, 
can be parts of a dioxolane ring. 
Examples of individual phenols which can be employed according to the 
invention are: phenol, o-cresol, m-cresol, p-cresol, xylenols, 
4-chlorophenol, hydroquinone, resorcinol, 1-naphthol, 2-naphthol, 
1,5-dihydroxynaphthalene, 4,4'-methylene-bis-phenol, 
1,1-bis-(4-hydroxyphenyl)-ethane, 2,2-bis-(4-hydroxyphenyl)propane, 
4,4'-cyclohexylidene-bisphenol, 4,4'-dihydroxydiphenyl ether, 
4,4'-dihydroxydiphenyl sulphone, 4,4'-dihydroxydiphenylsulphone, 
2-sec.-butylphenol, 3-sec.-butylphenol, 3,5-di-i-propylphenol, 
3,4-dimethylphenol, 3,5-dimethylphenol, 3,5-di-tert.-butylphenol, 
3-methylphenol, 3-(2-pentyl)-phenol, 3-(3-pentyl)-phenol, 
3,4,5-trimethylphenol, 2-i-propylphenol, 3-i-propylphenol, 
3-tert.-butylphenol, 3-methyl-5-i-propyl-phenol, 1-naphthol, 
5,6,7,8-tetrahydro-1-naphthol, 3,4-dimethyl-6-chlorophenol, 
2-chlorophenol, 3,5-dimethyl-4-dimethylaminophenol, 
3,5-dimethyl-4-diallylamino-phenol, 3,5-dimethyl-4-methyl-thiophenol, 
2-methyl-4-dimethylamino-phenol, 2-isopropoxy-phenol, 3-amino-phenol, 
amino-phenols in which the NH.sub.2 group is protected in the form of the 
acetate or in the form of an imine or amidine salt or in the form of the 
methyl-carbamate, 2-(1',3'-dioxolan-2'-yl)-phenol, 
2-(4',5'-dimethyl-1',3'-dioxolan-2'-yl)-phenol, 
3-methyl-4-dimethylamino-phenol, 2-thiobutylphenol, 
2-thioethyl-methyl-phenol, 3,5-dimethyl-4-(N,N-dimethylamino)-phenol, 
3,5-dimethyl-4-amino-phenol, 2-tert.-butyl-5-methyl-dimethylamino-phenol, 
2-(N-methyl-N-propinyl)-amino-phenol, 2-allyloxy-phenol, 2-hydroxy-phenol, 
2,3-hydroxy-phenol, 3-trimethylsilylphenol and polyhydroxyphenols in which 
all of the OH groups except one are protected, for example in the form of 
the acetal of acetone, in the form of a mixed acetal of chloroacetaldehyde 
or in the form of a mixed ethyl ester of phosphoric acid, and also 
1-quinolin-8-ol, 2-methyl-1-quinolin-8-ol, benzothiophen-4-ol, 
2,2-dimethyl-7-benzofuranol, 
4-chloro-2,3-dihydro-2,2-dimethyl-7-benzofuranol and 
3,4-dihydro-2,2-dimethyl-benzopyran-8-ol. 
The process according to the invention is illustrated with the aid of the 
following equation, taking, as an example, the reaction of phenol with 
phosgene in the presence of an organic phosphorus compound: 
##STR1## 
The organic phosphorus compound to be employed according to the invention 
is used in an amount of, for example, 0.1 to 20 mol %, preferably 0.2 to 
10 mol % and particularly preferentially 0.5 to 5 mol %, based on each 
phenol equivalent employed. 
Under the action of the additives according to the invention, comprising an 
organic phosphorus compound, phosgene is used in a molar ratio of 1:1 to 
2:1, preferably 1:1 to 1.5:1 and particularly preferentially 1:1 to 1.2:1, 
based on each phenol equivalent employed. It is possible to use less than 
the stoichiometric amount of phosgene, but in general this is of no 
advantage since, in this case, unconverted phenol has to be separated off 
and the yield falls. The use of larger amounts of phosgene is possible, 
but brings no further advantages. 
The process according to the invention is carried out in a homogeneous 
liquid phase. The melt of the phenols described, or a solution of the 
phenols described, can, for example, be regarded as a homogeneous liquid 
phase. If the reaction is carried out in solution, the solvent employed 
can be, for example, an aliphatic or aromatic hydrocarbon, such as 
pentane, hexane, cyclohexane, toluene, xylene or benzene, a halogenated 
hydrocarbon, such as trichloroethane, chlorobenzene or dichlorobenzene, or 
an ester, such as ethyl acetate or butyl acetate. Preferably, a 
halogenated hydrocarbon is employed, and particularly preferentially 
chlorobenzene is employed. 
Preferably, the reaction is carried out without a solvent and only in the 
melt of the phenol. The space-time yield achieved in this way is higher 
than that otained when the reaction is carried out in the presence of a 
solvent. However, it can be advantageous to carry out the reaction in a 
solvent when the melting point of the phenol to be employed is above the 
desired reaction temperature and the phenol therefore, at least at the 
start of the reaction, would react only slowly with the phosgene if the 
solvent were not present. The presence of a solvent can also be 
advantageous for controlling and removing the heat of reaction of the 
exothermic reaction. 
The reaction of the process according to the invention is carried out in 
the temperature range of 60.degree. to 180.degree. C., preferably of 
80.degree. to 160.degree. C. and particularly preferentially of 
100.degree. to 140.degree. C. 
The reaction can be carried out under normal pressure or under elevated 
pressure. The rise in the partial pressure of phosgene in the reaction 
mixture under elevated pressure within a closed apparatus increases the 
rate of reaction. However, due to the formation of hydrogen chloride as 
the reaction proceeds, the total pressure in a closed apparatus rises 
sharply and this demands additional expenditure on apparatus and safety 
measures. In general, therefore, the reaction will be carried out under 
atmospheric pressure or under only a slightly elevated pressure, for 
example up to 10 bars, and the hydrogen chloride can be removed 
discontinuously or continuously from the pressure apparatus. 
The process according to the invention can be carried out continuously or 
discontinuously. A continuous process can be carried out, for example, in 
a reaction tube, in a stirred kettle cascade, in a loop reactor or in a 
counter-current column. 
To carry out the process according to the invention, the phenol and the 
intended organic phosphorus compound can, for example, be initially 
introduced and brought to the desired reaction temperature, with melting. 
Phosgene is passed in at this temperature, so that only a gentle reflux of 
phosgene takes place in the reflux condenser fitted on the apparatus. The 
evolution of hydrogen chloride is then observed using a bubble counter or 
another suitable device. The reaction has ended when the evolution of 
hydrogen chloride ceases. The reaction mixture is then separated by 
distillation into the desired chloroformic acid ester and a residue. This 
residue contains the organic phosphorus compound. The organic phosphorus 
compound has not lost its effectiveness for the process according to the 
invention as a result of this procedure. It can therefore be employed for 
a further run of the process according to the invention. For this purpose, 
the bottom product from the distillation of the first reaction run can be 
worked up, for example by further distillation or by suitable 
recrystallization, to give the pure organic phosphorus compound, which is 
then available for a further reaction run. In a further variant of the 
process according to the invention it is, however, also possible to use 
the distillation bottom product from the first reaction run, which 
contains the organic phosphorus compound which is still effective, 
unchanged in a second reaction run. Because of the simplicity, this latter 
variant is preferred. It is, however, also possible partly to remove 
by-products which may have formed and remain in the residue and to recycle 
only a portion of the residue, with the organic phosphorus compound 
contained therein, into a subsequent batch. The repeated use of the 
organic phosphorus compound can be carried out, for example, 2 to 15 
times, preferably 2 to 10 times, and particularly preferentially 3 to 6 
times. Such repeated use of the organic phosphorus compound is 
particularly significant when the process according to the invention is 
carried out continuously. In this case it is then possible, for example, 
to feed the reaction mixture, which has been removed from the continuously 
operated reactor and in which the reaction has not necessarily been 
carried out to complete conversion, into a continuously operated 
distillation apparatus. In this continuous distillation, the desired 
chloroformic acid aryl ester is removed as the top product, whilst the 
bottom product, at least in part, is recycled into the starting mixture 
for the process according to the invention. 
Examples which may be mentioned of chloroformic acid aryl esters which can 
be prepared by the process according to the invention are: chloroformic 
acid phenyl ester, chloroformic acid o-cresyl ester, chloroformic acid 
m-cresyl ester, chloroformic acid p-cresyl ester, chloroformic acid 
dimethylphenyl ester, chloroformic acid 4-chlorophenyl ester, chloroformic 
acid naphthyl ester, hydroquinone bis-chloroformate, resorcinol 
bis-chloroformate, 1,5-dihydroxynaphthalene bis-chloroformate, 
4,4'-methylenebisphenyl bis-chloroformate, 
1,1-bis-(4-hydroxyphenyl)-ethane bis-chloroformate, 
2,2-bis-(4-hydroxyphenyl)-propane bis-chloroformate, 
4,4'-cyclohexylidene-bisphenyl bis-chloroformate and 
4,4'-dihydroxydiphenyl ether bis-chloroformate. 
The chloroformic acid aryl esters, and in particular chloroformic acid 
phenyl ester, are obtained in high purity by the process according to the 
invention. They can therefore be further used in the form of the crude 
products for many purposes. Of course, they can also be further purified 
in a known manner, for example by distillation or recrystallization. 
Chloroformic acid aryl esters are valuable intermediate products, for 
example in the preparation of dyestuffs, such as Sirius dyestuffs (German 
Offenlegungsschrift No. 2,325,088 and Ullmanns Enzyklopadie der 
technischen Chemie (Ullmann's Encyclopaedia of Industrial Chemistry), 
Volume 4, pages 105, 108 and 109, Urban and Schwarzenberg, 3rd Edition, 
Berlin-Munich, 1953) and for the preparation of polycarbonate plastics, 
bactericides and plant protection agents, such as herbicides and 
insecticides, especially of the category comprising the carbamates, such 
as are listed, for example, in "The Pesticide Manual (British Crop 
Protection Council), 6th Edition, 1979" or in K. H. Buchel, 
"Pflanzenschutz und Schadlingsbekampfung" ("Plant Protection and Pest 
Control") (G. Thieme Verlag, 1977, pages 60-72). 
Particular mention may be made of the compounds which are listed under the 
following tradenames and "common names": Sevin (carbaryl), mexacarbate, 
Methiocarb, Baycarb, Aminocarb (Matacil), propoxur (Baygon), Carbanolate, 
promecarb, Mobam, Allyxycarb (Hydrol), butacarb, carbofuran, Formetamate 
hydrochloride, Meobal, Metacrate, bufencarb, Dioxacarb, Macbal, Landrin, 
CMPO, Isoprocarb, Sapecron, TBPMC, bendiocarb, Ethiofencarb, Hercules 6007 
and Promacyl. 
Such carbamates can also be obtained by reacting phenols with carbamoyl 
halides or isocyanates. However, carbamoyl halides are compounds which 
give cause for concern from the standpoint of work hygiene (see discussion 
supra). With isocyanates initially only those carbamates which carry a H 
atom on the carbamate N atom are obtained; the reaction of chloroformates 
with amines is not subject to this restriction, so that this synthesis 
route has particular advantages, very particularly for the preparation of 
carbamates which are disubstituted on the carbamate N atom. The intended 
uses mentioned are known to those skilled in the art and are described, 
for example, in (German Auslegeschrift No. 2,131,555, German 
Auslegeschrift No. 1,213,419 and Ullmann's Enzyklopadie der technischen 
Chemie (Ullmann's Encyclopaedia of Industrial Chemistry), 4th Edition, 
Volume 9, page 383, Verlag Chemie 1975. 
Compared with the prior art, the process according to the invention offers 
the following advantages: higher yields and purer products are obtained; 
there is less corrosion and are also fewer ecological problems and 
problems with regard to work hygiene; the reaction can also be carried out 
without applying pressure and the effect of this is higher safety in 
process control; if the reaction is carried out without additional solvent 
a higher space-time yield is achieved; the opportunity for repeated use of 
the organic phosphorus compounds according to the invention lowers the 
cost of the process. 
It is surprising that the organic phosphorus compounds according to the 
invention effect the reaction of the phenol with the phosgene to give the 
chloroformic acid aryl ester but do not promote the further condensation 
to the diaryl carbonate. Surprisingly, the additives according to the 
invention are superior or at least equivalent to the known additives 
according to the prior art, in respect of their effect on the reaction, 
but additionally display the technical advantages indicated.

COMISON EXAMPLES 
Example 1 
(Method according to German Auslegeschrift No. 2,131,555, Example 1) 
A mixture of 500 g (5.32 mols) of phenol and 10 to 20 g of 
dimethylformamide is heated to 100.degree. to 120.degree. C. in a 
round-bottomed flask which is provided with a stirrer, a gas inlet tube, 
an internal thermometer and a reflux condenser cooled to -30.degree. to 
-40.degree. C., with a bubble counter in the gas line. Phosgene is passed 
in slowly, so that there is--only just--no reflux in the reflux condenser. 
The contents of the flask become dark in colour. 
The reaction is substantially complete when permanent reflux of COCl.sub.2 
is observed. The reaction mixture is then stirred for a further 1/2 to 1 
hour, or the reflux condenser is removed and further phosgene is passed 
through the mixture (10 to 20% excess). 
Excess phosgene is blown out of the reaction mixture with nitrogen, and 
chloroformic acid phenyl ester is distilled off in vacuo (boiling point 
85.degree. C./20 mm Hg). 
761.5 g of a product which is 99.5% pure (according to titration with 
di-n-butylamine) are obtained (91% of the theoretical yield). 
According to analysis by gas chromatography, this product contains about 
0.1 to 0.2% of dimethylcarbamoyl chloride. 
Example 2 
(Method according to Japanese Application No. 23,409/67) 
94 g (1 mol) of phenol and 8.3 g of triethyl phosphite are initially 
introduced into an apparatus as in Example 1 and the mixture is liquefied 
by melting and allowed to cool to 35.degree. C. The mixture solidifies 
again on cooling. Phosgene is passed in until reflux takes place. No 
evolution of HCl is observed in the bubble counter; thus, no substantial 
reaction takes place. 
Example 3 
The procedure is as described in Example 2, but the mixture is heated to 
120.degree. to 125.degree. C. and about 60 g of COCl.sub.2 are introduced 
in the course of 8 hours. 
Excess COCl.sub.2 is blown out and 104 g of crude product are obtained; 
this product solidifies on standing. 
The product contains about 15% of chloroformic acid phenyl ester (this 
corresponds to a yield of 10% of the theoretical yield) and essentially 
consists of diphenyl carbonate (according to analysis by gas 
chromatography). 
EXAMPLES ACCORDING TO THE INVENTION 
Example 4 
(a) 500 g (5.32 mols) of phenol and 28 g of triphenylphosphine are 
initially introduced into an apparatus as described in Example 1, the 
mixture is warmed to 120.degree. to 125.degree. C. and phosgene is passed 
in at this temperature. 530 g of COCl.sub.2 are consumed within 8 to 10 
hours. The reaction mixture is stirred for a further 1 hour at 125.degree. 
C., the reflux condenser is then replaced by a gas inlet tube and excess 
COCl.sub.2 is blown out with nitrogen. 
In contrast to the method according to Examples 1 and 3, the reaction batch 
is still colourless to pale yellow, even at this stage. 
The reaction mixture is distilled in vacuo at 74.degree. to 79.degree. 
C./12 mm Hg up to an internal temperature of 105.degree. C., and 744 g of 
chloroformic acid phenyl ester are obtained (purity 99.6% according to 
titration against amine; yield 89.5% of the theoretical yield). 
(b) A further 500 g of phenol are added to the residue, which weighs 100 g, 
without feeding in fresh triphenylphosphine. The reaction is carried out, 
as described under 4(a), with 560 g of COCl.sub.2. After a phosgenation 
time of 8 hours, 764 g of distilled 99.7% pure chloroformic acid phenyl 
ester are obtained (91.5% of the theoretical yield). 
(c) The distillation residue is re-used with 500 g of phenol and 540 g of 
phosgene, without the use of fresh triphenylphosphine. After a 
phosgenation time of 10 hours, 754 g of distilled chloroformic acid phenyl 
ester are obtained (purity 99.8%; yield 90.4% of the theoretical yield). 
A distillation residue which is of low viscosity, weighs about 200 g and 
still contains 25% of chloroformic acid phenyl ester remains; the 
remainder is essentially diphenyl carbamate. The yield after 3 cycles is 
thus 2,262 g; purity about 99.7% (90.3% of the theoretical yield) in the 
distillate and, in addition, about 50 g in the residue (2.0% of the 
theoretical yield). 
Example 5 
The procedure is as described in Example 4(a), but only 7.0 g of 
triphenylphosphine are used and 550 g of COCl.sub.2 are passed in at about 
145.degree. C. 
After a reaction time of about 14 hours, distillation yields 640.6 g of 
99.6% pure chloroformic acid phenyl ester and 147.2 g of residue, which 
still contains 28.4% of ester. The total yield is thus 638.0 g (76.6% of 
the theoretical yield) with, in addition, 41.8 g in the residue (5.0% of 
the theoretical yield). 
Example 6 
Phosgene is passed into a batch such as is described in Example 4(a), 
initially without warming, until sufficient COCl.sub.2 is present in the 
apparatus to boil under reflux. The gas inlet is shut off and the mixture 
is warmed slowly. 
At an internal temperature of from 60.degree. C., escaping HCl gas can be 
detected at the condenser outlet; this means that the reaction already 
proceeds at this temperature. 
At an internal temperature of from 80.degree. C. the reflux of COCl.sub.2 
in the condenser also ceases, since the reaction proceeds sufficiently 
rapidly to consume the available supply of COCl.sub.2 within a few 
minutes. 
Example 7 
(a) The procedure is as described in Example 4(a), but 30 g of technical 
grade triphenylphosphine oxide are used in place of triphenylphosphine. 
530 g of COCl.sub.2 are taken up during a reaction time of 12 hours. 
On distillation, 718 g of chloroformic acid phenyl ester are obtained 
(purity 99.5%; yield 85.7% of the theoretical yield). 
(b) The residue, which weighs 110 g, is introduced, without the addition of 
further triphenylphosphine oxide, into a new batch of 500 g of phenol. 550 
g of COCl.sub.2 are taken up within 12 hours. The condenser is removed and 
a further 100 g of COCl.sub.2 are passed through the batch. On 
distillation, 733.1 g of chloroformic acid phenyl ester are obtained 
(purity 99.2%; yield 87.4% of the theoretical yield). A residue which is 
of low viscosity when hot, weighs 170 g and still contains 25% of 
chloroformic acid ester remains. The remainder is essentially diphenyl 
carbonate. 
The total yield is thus 1,442 g (86.6% of the theoretical yield) with, in 
addition, 42.5 g (5.1% of the theoretical yield) in the residue. 
Example 8 
The procedure is as in Example 7(a), but the COCl.sub.2 is passed in at 
110.degree. C. 
After a phosgenation time of 13 hours, 530 g of COCl.sub.2 had been 
consumed. 
On distillation, 745 g of chloroformic acid phenyl ester are obtained 
(purity 99.8%; yield 89.3% of the theoretical yield). 
A residue remains which weighs 83.5 g and still contains 40% of 
chloroformic acid phenyl ester (33.4 g; 4.0% of the theoretical yield). 
Examples 9-13 
Examples with further catalysts, which were carried out in accordance with 
Example 4(a), are summarised in the Table which follows. 
TABLE 
__________________________________________________________________________ 
React- 
Phos- (% of the theo- 
tion gene Reac- 
Yield 
(g) Yield 
retical yield) 
Feed temper- 
consum- 
tion 
in the 
in the 
in the 
in the 
Ex- (g of ture ption 
time 
distil- 
resi- 
distil- 
resi- 
ample 
phenol) 
Catalyst Amount 
(.degree.C.) 
(g) (hours) 
late 
due late 
due total 
__________________________________________________________________________ 
9 250 1-Phenyl-2,5- 
10.2 g 
120-130 
300 17 370.8 
3.6 
89.1 
0.9 90.0 
dihydro-2-methyl- 
phosphol oxide 
10 500 C.sub.6 H.sub.5 --PCl.sub.2 
34.1 g 
120-125 
510 10 604.7 
64.5 
72.6 
7.7 80.4 
11 500 (C.sub.6 H.sub.5).sub.3 P(CH.sub.3)Br 
39.1 g 
120-125 
555 11 713.7 
40.4 
85.7 
4.9 90.6 
12 500 (n-C.sub.4 H.sub.9).sub.3 P 
21.5 g 
120-125 
560 15 729.3 
43.2 
87.6 
5.2 92.8 
13 500 (C.sub.6 H.sub.5).sub.3 PCl.sub.2 
35.5 g 
120-125 
520 8.5 774.2 
26.4 
93.0 
3.2 96.2 
__________________________________________________________________________ 
EXAMPLE 14 
385.7 g (3.0 mols) of p-chlorophenol and 16 g of triphenylphospine are 
initially introduced into a 1 l flask which is fitted with a stirrer, a 
gas inlet tube, an internal thermometer and a reflux condenser with 
intense cooling. The mixture is heated to 125.degree. C. and, in the 
course of 16 hours, a total of 310 g of COCl.sub.2 are passed in so slowly 
that phosgene just does not start to boil under reflux. After removing the 
condenser, residual phosgene is driven off with nitrogen and final 
residues are then removed in vacuo. 
Crude chloroformic acid 4-chlorophenyl ester is obtained in a yield, 
according to titration against amine, of 85% of the theoretical yield, in 
the form of a pale yellow melt which solidifies on cooling. 
Pure ester is obtained by distillation (boiling point 104.degree. C./10 mm 
Hg). 
EXAMPLE 15 
324.4 g (3.0 mols) of p-cresol and 15.7 g of triphenylphosphine are 
initially introduced into an apparatus as described in Example 1, the 
mixture is heated to 120.degree. to 125.degree. C. and 330 g of COCl.sub.2 
are introduced in the course of 12 hours. The reaction mixture is stirred 
for a further 1 hour, excess phosgene is drawn off in vacuo and 461.0 g of 
chloroformic acid 4-tolyl ester are distilled off; according to titration 
against di-n-butylamine and according to analysis by gas chromatography 
this ester is virtually pure (boiling point 92.degree. to 94.degree. C./13 
mm Hg). The yield is 90.1%; small amounts are still present in the 
distillation residue. 
EXAMPLE 16 
433 g (3.0 mols) of 2-naphthol and 15.7 g of triphenylphosphine are 
initially introduced into an apparatus as described in Example 1. The 
mixture is heated to 120.degree. to 125.degree. C. and 325 g of COCl.sub.2 
are introduced in the course of 12 hours. The reaction mixture is stirred 
for a further 1 hour, excess phosgene is drawn off in vacuo and crude 
chloroformic acid 2-naphthyl ester is obtained in a yield of 75% of the 
theoretical yield. 
It can be purified by vacuum distillation (boiling point 136.degree. to 
138.degree. C./7.5 mm Hg or 121.degree. to 124.degree. C./1.5 mm Hg). 
An adequate result is obtained when 1-naphthol is reacted instead of 
2-naphthol. 
EXAMPLE 17 
125 g of phosgene are passed, in the course of 7 hours, into a solution of 
114.0 g (0.5 mol) of 2,2-bis-(4-hydroxyphenyl)-propane ("bisphenol A") and 
5.0 g of triphenylphosphine in 1 l of chlorobenzene at 120.degree. to 
125.degree. C. at a rate such that COCl.sub.2 does not condense or 
condenses to only a slight extent in a reflux condenser which is connected 
to the reaction vessel and is cooled with CO.sub.2. The reaction mixture 
is then stirred for 2 hours at 115.degree. C. The solvent is distilled off 
in a rotary evaporator. 
190.7 g of 90.0% pure 2,2-bis-(4-choroformoxyphenyl)-propane are obtained 
(97.2% of the theoretical yield); (purity determined by titration with 
di-n-butylamine). 
The mass spectrum of a sample recrystallised from naphtha shows signals at 
m/e=352/354 ("molecular peak") and the NMR spectrum (in CDCl.sub.3) shows 
signals at .delta.=1.67 (s), 7.1 (d) and 7.3 (d) ppm. 
EXAMPLE 18 
500 g of 2-sec.-butylphenol (99% pure;=3.30 mols) and 5.8 g of 
triphenylphosphine are initially introduced into an apparatus as described 
in Example 1. The mixture is heated to 140.degree.-145.degree. C. and 360 
g of phosgene are introduced in the course of 6.5 hours. The reaction 
mixture is stirred for a further 1 hour and worked up as described in 
Example 1. 
Distillation yields 669.5 g of pure chloroformic acid 2-sec.-butyl-phenyl 
ester which has a boiling point of 116.degree.-118.degree./16 mm Hg 
(literature: 71.degree./1 mm Hg; (German Offenlegungsschrift No. 
2,213,408) and is 100% pure; the purity of the ester can be determined by 
titration against amine. 
This corresponds to a yield of 95.5% of the theoretical yield. 
A residue weighing 31 g remains and this still contains the product in an 
amount making up about 50% of its weight. The catalyst remains in the 
disillation residue and can be re-used with this in a subsequent reaction 
batch, without any loss in activity being observed.