Sartori The War Gases Chemistry and analysis

104 HALOGEN ATED ESTERS OF ORGANIC ACIDS

Water and alkalies decompose it, forming hydrocyanic acid, carbon dioxide and methyl alcohol 1 :

/OCH3

CO( + H,O = HCN + CO8 + CH3OH

With aniline, methyl chloroformate reacts as follows z :

/OCH3		/OCH3		+ HC1
C0<	+ C6H5NH2	= C0(
NC1			NNHC6H5
This reaction forms the basis		of a method		for the quantitative

determination of methyl chloroformate which consists essentially in treating the substance to be tested with aniline solution and titrating the hydrochloric acid formed. In this case it is not possible to determine the carbamic ester formed gravimetrically (as in the phosgene estimation), for it is very soluble in water.3

Though methyl chloroformate is a powerful lachrymator, it was not used alone as a war gas.

Because of its strongly irritant properties, it has been used in insecticidal preparations : " Zyklon A," which is a mixture of 90% of methyl cyanoformate and 10% of methyl chloroformate, and " Zyklon B," a mixture of liquid hydrocyanic acid and irritant chlorinated and brominated compounds.4

3. Mono-, diand tri-chloromethyl Chloroformates

These compounds were prepared by Hentschel in 1887 5 by the action of chlorine on methyl chloroformate.

During the war of 1914-18 they were employed as war gases, especially :

The mixture of monochloromethyl chloroformate with dichloromethyl chloroformate, used in 1915 by the Germans under the name of " K-Stoff," and later also by the Allies, especially the French, by whom it was called " Palite."

Trichloromethyl chloroformate, used almost exclusively by the Germans, under the name of " Perstaff" (Meyer).

The manufacture of these substances was carried out by the formate method or the chloroformate method, as mentioned on p. 99. The method of chlorination in each of these is similar and requires a suitable source of light. Many experiments on this subject have indicated that the Osram £-watt arc lamp and

the mercury vapour lamp are suitable light		sources, and the
1 NEF, Ann., 1897, 287, 290.
1	WILM and WISCHIN, Ann., 1868, 147, 157.
3	VLES, Rec. trav. chim., 1934, 53, 964.
4	FRICKHINGER, Case in der Schddlingsbekatnpfung,	Berlin, 1933, 27.
5	HENTSCHEL, /. prakt. Chem., 1887, 36,99,

THE CHLOROMETHYL CHLOROFORMATES 105

latter is to be preferred owing to its light being rich in ultraviolet radiation.1

By this means a mixture of the three chloro-derivatives is generally obtained, and these may be separated by fractional distillation :

Monochloro-derivative	.	b.p. 106-5° to 107°C.
Dichloro-derivative .	.	b.p. 110° to 111°C.
Trichloro-derivative .	.	b.p. 127-5° to 128°C.

Separation of the monoand dichloro-derivatives is difficult because of the closeness of their boiling points, but the trichlorocompound is very easily separated from the monoand dichlorocompounds.

LABORATORY PREPARATION

Various Chloro-derivatives.2 100 gm. methyl formate are placed in a 250 ml. flask fitted with a reflux condenser and a glass inlet tube for chlorine, and the whole weighed. The contents of the flask are heated to boiling and then a current of chlorine introduced, exposing the reacting substances to direct sunlight as far as possible, or to the light from a soo-watt lamp. By properly regulating the temperature and the addition of the chlorine and occasionally weighing the flask and its contents it is possible to obtain any of the chloro-derivatives. The reaction-product is fractionally distilled under reduced pressure.

Trichloromethyl Chloroformate.3 100 ml. of methyl formate are placed in a flask connected by a ground-glass joint with a condenser containing ice and salt. From the commencement the flask is exposed to a 5oo-watt lamp, and the current of chlorine then started and maintained at a very low speed in the

early phase, so that the		temperature is maintained	at 30° C.
As the reaction proceeds		the rate of addition of the	chlorine is
gradually increased, so		that the temperature finally reaches
about 90° C.	The chlorination is complete after about 30 hours.
The product	obtained is distilled under reduced pressure in an

all-glass apparatus provided with a fractionating column and a condenser. The middle fraction, boiling between 50-0° and 50-4° C. at 48 mm., is collected in a receiver containing calcium chloride. In order to purify the product it is redistilled. Yield about 70% of theoretical.4

1GRIGNARD, Compt. rend., 1919, 169, 1074 ; A. KLING and coll., Compt. rend., 1919, 169, 1046.

2HENTSCHEL, /. prakt. Chem., 1887, 36, 213-305 ; FLORENTIN, Butt. soc.

chim., 1920, 27, 97 ; BARTHELEMY, Rev. prod, chim., 1922, 25, 685.

3 RAMSPERGER and WADDINGION, /. Am. Chem. Soc., i933> 55, 214. * STOLZENBERG, op. cit.

106 HALOGENATED ESTERS OF ORGANIC ACIDS

INDUSTRIAL MANUFACTURE

During the war of 1914-18 both of the methods described were

used—the formate method and the chloroformate method.

The Formate Method.

This

method was used

in

the

Bayer

plants

in

Germany.

It

was

very

costly,

chiefly

because

concentrated formic acid was

needed for the preparation of

the formate.

The* methyl

formate was

obtained

as

described

on

s»^

page

101,

and was

chlori-

L

L

fl

nated

in

special

vessels

A

(Fig. 6), 2-3 m. in diameter

B

and

1-5 m. in

height, fitted

5

with

an agitator

B.

These

n-

r-i

n

vessels were of cast iron, lined

^=>

° » « « ° «=^

FlG 6

with lead, or often

enamelled.

The gaseous chlorine

was led

in at the

bottom

of

the vessel

through

the pipe

C and

the

reaction

accelerated

by

employing

eight

Osram

lamps

(L)

of

4,000 candle-power, placed in the upper part

of

the

vessel.

The heating of the

reaction-mass

is

carried

out

by

means

of

steam coils or by the electrical resistances, S.

In order to obtain the less highly chlorinated products the reaction is suitably regulated and lamps of a lower intensity employed. By chlorinating more vigorously, however, and using a mercury-vapour lamp it is very easy to obtain the trichlorocompound.

After the chlorination the product is distilled in special vessels

FIG. 7.

lined with porcelain (Fig. 7) heated by the coils B. The fraction boiling at lower temperatures is condensed in Sl (cooled by

MONOCHLOROMETHYL CHLOROFORM ATE 107

water) and 52 (cooled by ice), and then collected in the receiver R. The more highly chlorinated product remains in A.

The Chloroformate Method. This method is less expensive and more suited to large-scale manufacture than the preceding. It was used in Germany by the Hoechst works and later also in France.

The chlorination of the chloroformate, obtained by the method given on p. 102, was carried out like that of methyl formate, in lead-lined or enamelled vessels. The lids of these vessels were also enamelled and carried eight Osram lamps protected by glass bells. The chlorine was introduced through eight pipes.

According to Grignard, the chlorination must commence in the gaseous phase, and so the methyl chloroformate is first heated in such a way as to produce a slight pressure, then the lamps switched on and the chlorine then introduced at such a rate as to prevent the reaction from being violent. The product may be rectified as described in the preceding method.

PHYSICAL AND CHEMICAL PROPERTIES

The chloro-derivatives of methyl chloroformate are all colourless liquids at ordinary temperatures, have boiling points close together and dissolve easily in organic solvents. All are hydrolysed by water even at ordinary temperatures and react

readily with various compounds.
(a) MONOCHLOROMETHYL		CHLOROFORMATE		(M.Wt. 128-9)
		C1COOCH2C1.
This is a mobile, colourless liquid with an				irritating	odour,
which boils at 106-5° to		107° C. at ordinary		pressure	and at
52-5° to 53° C. at	100 mm. of mercury.		It has a S.G. of 1-465 at
15° C., while its	vapour	density is 4-5	(air =	i). The	vapour

tension at 10° C. is 3-6 mm. and at 20° C. 5-6 mm. Monochloromethyl chloroformate is hydrolysed by water at

ordinary temperatures ; this decomposition takes place more rapidly and completely by the action of hot water or in the presence of alkali. Formaldehyde, hydrochloric acid and carbon dioxide are formed :

/OCH2C1

C0< + HaO = HCHO + 2 HC1 + CO2 XC1

This behaviour of the monochloro-derivative is applied in the identification and quantitative determination in air of the industrial product (see pp. 123, 124).

io8 HALOGENATED ESTERS OF ORGANIC ACIDS

Monochloromethyl chloroformate, like phosgene, liberates iodine from sodium iodide, but the reaction is not quantitative, proceeding only to about 70% completion.1

/OCH2C1

CO^ + 2 Nal = CH2O -{- I2 + CO+ 2 NaCl

Like methyl chloroformate, but unlike the diand tri-chloro- derivatives, it does not liberate bromine from lithium bromide.

Ferric chloride and anhydrous aluminium chloride decompose chloromethyl chloroformate even in the cold, while on heating to about 70° C. the reaction is more rapid,2 phosgene being formed.

/OCH2C1	-»-COCl2 + CH2O
CO<
NC1

Alcohols react energetically, giving hydrochloric acid and the corresponding monochloromethyl carbonate :

/OCH..C1		/OCH2C1
C0<NC1	+ R-OH	= C0( XOR	+ HC1

With sodium phenate, reaction takes place at the ordinary temperature with formation of sodium chloride and phenyl

monochloromethyl carbonate :
/OCH2C1		/OCH2C1
C0(	+ C6H6-ONa = C0<	+ NaCl
\fM		\*~kf> TT
V~l		L-'L-g-TlE

Monochloromethyl chloroformate, unlike methyl chloroformate, reacts with difficulty with chlorosulphonic acid, forming monochloromethyl chlorosulphonate only after boiling on the water bath for 4 hours 3 :

OCH2C1	/OH	/OCH2C1
		+ HC1 + C02

This is a colourless liquid, boiling at 49° to 50° C. at a pressure of 14 mm. of mercury ; its S.G. is 1-63 at room temperature. It has powerful irritant properties.4

By the action of methyl sulphuric acid on monochloromethyl

1A. FERRET, Bull. soc. chim., 1936, 957.

2A. KLING and D. FLORENTIN, Compt. rend., 1919, 169, 1166.

* M. KRAFT and ALEXEJEV, /. Obscei Khim., Ser. A., 1932, 64, 726. * FUCHS and KATSCHER, Ber., 1927, 60, 2292.

DICHLOROMETHYL CHLOROFORMATE

109

chloroformate, methyl chlorosulphonate is formed (see p. 266), according to the following (Kraft) :

/OCH8C1		/OCH3	/OCH3
C0<	+ S02(	= S02<	+ HC1 + C02 + CH20
XC1		NOH	NC1

Monochloromethyl chloroformatealso reacts with benzoic acid, forming monochloromethyl benzoate (Kraft) :

/OCH2C1

CO( + C6H5COOH = C6H5COOCH2C1 + HC1 + CO2

The toxicity of monochloromethyl monochloroformate is relatively slight. Its lachrymatory power is, however, considerable ; the minimum concentration capable of producing lachrymation is 2 mgm. per cu. m. of air. The limit of insupportability is 50 mgm. per cu. m. of air (Flury).1

(b) DICHLOROMETHYL CHLOROFORMATE

(M.Wt. 163-4)

C1.CO.OCHC12.

Colourless liquid, boiling at no0 to 111° C. at 760 mm., and at 54° to 55° C. at a pressure of 100 mm. of mercury. Its S.G. is 1-56 at 15° C., and its vapour density is 5-7 (air = i).

The vapour tension varies with the temperature as shown in the following table :

TEMPERATURE	VAPOUR TENSION
0 C.	MM. MERCURY
10	3-6
20	5
30	6

This compound in contact with water decomposes as follows :

Cl—COOCHC12 + H2O = CO + CO2 + aHCl.

The hydrolysis proceeds fairly rapidly, even in the cold, but is much accelerated by heating and even more so by addition of alkali.

Dichloromethyl chloroformate reacts with cold potassium iodide, liberating iodine :

/
C0<XC1	+ 3 KI = 3 KC1 + HI + 2 CO + I2

In this reaction carbon monoxide is evolved quantitatively.2

1	FLURY, Z. ges.exp. Med., 1921, 13, 567.
2	A. FERRET and J. BIECHLER, Compt, rend., 1936, 86.

no HALOGENATED ESTERS OF ORGANIC ACIDS

The dichloro-compound reacts with lithium bromide (unlike the monochloro-derivative} x :

OCHC12

+ 2 LiBr = 2 CO+ 2 Lid + HC1 + Br2

Ferric chloride and anhydrous aluminium chloride decompose dichloromethyl chloroformate slowly at ordinary temperatures and rapidly at 80° C., forming a mixture of carbon dioxide and chloroform 2 :

Cl—COOCHC12 = C02 + CHC13.

Like the preceding compound, it reacts with alcohols, forming hydrochloric acid and the corresponding dichloromethyl carbonate :

/OCHC12		/OCHC12
CO(NC1	+ R-OH = CO<	XOR	+ HC1

and with sodium phenate forming sodium chloride and phenyl dichloromethyl carbonate :

	/OCHClj		/OCHC12
	C0(	+ C6H5ONa = Nad +CO<
	Cl		XOC6H5
Aniline in aqueous or benzene solution reacts with
dichloromethyl		chloroformate to give	diphenylurea and
formanilide according to the equation :
/OCHCla		/NHC6H5	/NHC6H5	+ , HC,
C0<a	+ 3 C.H.-NH, - CO^.HJ + CO<H

Dichloromethyl chloroformate is less irritant than the preceding compound, but more toxic. Its limit of insupportability is 75 cu. mm. per cu. m. (Flury).

(c) TRICHLOROMETHYL CHLOROFORMATE	(M.Wt.197-85)
C1.CO.OCC13.

Colourless mobile liquid with an irritating odour slightly

reminiscent of phosgene. It is also known as " Diphosgene."
At ordinary	pressure it boils at 127-5° to 128°	C. and	at a
pressure of 18	mm. at 41° C. It solidifies at — 57° C. Its		S.G.
is 1-65 at 15° C.and its vapour density 6-9 (air = i).		Its refractive
index at 22° C. is 1-45664.

1 A. FERRET, Bull. soc. chim., 1936, 350.

a A. KLING and D. FLORENTIN, he. cit. ; GRIGNARD, RIVAT, etc., Compl. rend., 1919. 169. i°74. "43-

TRICHLOROMETHYL CHLOROFORMATE in

The variation of vapour tension with temperature is as follows (Herbst) :

TEMPERATURE	VAPOUR TENSION
° C.	MM. MERCURY
o	3
10	5
20	10-3
30	16-3

It dissolves in benzene and		in many other organic solvents.
At the ordinary temperature it		dissolves in 24 parts by weight
of phosgene.
On heating this compound it decomposes, forming phosgene
according to the equation * :
/OCC13		/Cl
C0<	-> 2 C0(
NC1		NC1

This decomposition takes place also at ordinary temperatures when trichloromethyl chloroformate comes into contact with substances having a porous structure such as activated carbon, or with iron oxide,2 etc.

Trichloromethyl chloroformate reacts with cold water very slowly, but hot water or alkalies accelerate this, hydrochloric acid and carbon dioxide being formed :

Cl—COOCC13 + 2H2O = 2CO2 + 4HC1.

By heating to boiling with alkali carbonates it decomposes to form sodium chloride and carbon dioxide :

Cl—COOCC18 + 2Na2CO3 =

With sodium iodide in acetone solution it reacts rapidly and quantitatively as follows :

/OCC13		+ 4 NaCl + 2 CO
CO<	+ 4 Nal = 2 I2
NC1

The reaction with lithium bromide is similar.3

Ammonia reacts vigorously, forming urea and ammonium

chloride :
	/OCC13		/NH2
	CO(NC1	+ 8 NH3 = 4 NH4C1 + 2 CO<NNH2
1 CAHOURS, Ann. Mm. phys., 1847, 352;			HENTSCHEL, /. prakt. Chem., 1887,
36, 99. 209 ; RAMSPERGER, /. Am. them. Soc., 1933, 55, 214.
1	H. P. HOOD and H. MURDOCH, /. Phys. Chem., 1919, 23, 498.
3	A. FERRET, Bull. soc. Mm., 1936, 350.

H2 HALOGENATED ESTERS OF ORGANIC ACIDS

With hexamethylene tetramine it reacts, like phosgene, to form an addition product of the formula x :

COC12.2(CH2)6N4.

Ferric chloride and anhydrous aluminium chloride decompose trichloromethyl chloroformate into carbon tetrachloride and carbon dioxide 2 :

/OCC13

C0( -* CC14 + CO,

VM'Cl

Trichloromethyl chloroformate does not react with concentrated hydrochloric acid.

With alcohols it reacts similarly to the other members of this group to form the corresponding trichloromethyl carbonate :

/OCC13		/OCC13
CO(	+ R-OH = CO(	+HC1
XI		XOR

However, if the alcohol is in excess and the reaction proceeds in the cold, its course is different 3 :

CC13	/OR
CR	+ 3 ROH = 2 CO< + 3 HC1
	XOR

The nature of the alcohol also affects the nature of the products formed. Thus with most primary alcohols the reaction described above takes place, but if there are present in the molecule of the primary alcohol radicles of high molecular weight, partial decomposition of the carbonate takes place with formation of phosgene and the corresponding chlorocarbonic ester, as follows * :

/OCC13		/Cl
C0<	-> COC12	+ C0<
NOR		XOR

With secondary alcohols the reaction proceeds similarly, but with tertiary alcohols a further decomposition of the chlorocarbonic ester formed takes place and carbon dioxide is evolved and the corresponding alkyl chloride is formed :

/C1

C0<N * RC1 -f CO2

V-ORVT

With excess of aniline in aqueous or benzene solution trichloromethyl chloroformate reacts like phosgene, being

1PUSCHIN and Mmc, Ann., 1937, 532, 300.

2KLING and coll., loc. cit.

•NEKRASSOV and MELNIKOV, /. prakt. Chem., 1930, 126, 81.

4NEKRASSOV and MELNIKOV, /. Rusk. Fis. Khim. Obsc., 1930, 62, 631, 1545.

/OCC13

4- C6H6-ONa = C0(N 4- NaCl OC6H5

TRICHLOROMETHYL CHLOROFORM.ATE 113

quantitatively transformed -into symmetrical diphenylurea or carbanilide 1 :

	/OCC13			/NHC6H5
	C0<	4- 4 C6H5-NH2 =		2 C0(	+4 HC1
	NC1			XNHC6H5
If,	however, there		is insufficient	aniline, a	mixture, of phenyl
isocyanate and anilido-formyl chloride is formed :
/OCC13			//N-C6H5			3HC1
CO(	+ 2 C6H5NH2		= C<	+ C6H5-NH-COC1 +
NC1			^O
With dimethyl aniline in presence of aluminium trichloride or
zinc chloride, Crystal Violet is formed.2
By	the	action	of trichloromethyl		chloroformate	on
diphenylamine, trichloromethyl N-diphenyl					urethane results,
together with a small quantity of tetraphenylurea 3 :
/OCC13			/OCC13
C0<	+ 2 (C6H5)aNH = CO^			4- (C6H5)2NH . HC1
CJ				N(C6H5)2

This urethane forms white crystals, melting at 61° C., which on heating to 200° to 250° C. decompose forming phosgene and diphenyl carbamic chloride. Cold water decomposes it into diphenylamine, hydrochloric acid and carbon dioxide.

Trichloromethyl chloroformate reacts with pyridine, forming a yellow crystalline substance of the formula * :

C5H5N(C1)CO(C1)NC6H5,

which decomposes by the action of water with evolution of carbon dioxide:

C8H6N(C1)CO(C1)NCBH5 4- H20 = 2(C6H5N.HC1) 4- CO2. Like the preceding compound, trichloro methyl chloroformate

reacts with sodium phenate, forming sodium chloride and phenyl trichloromethyl carbonate :

/OCC13

CO< NC1

In presence of an excess of the phenate the reaction proceeds further, diphenyl carbonate being formed 5 :

/OC6H5

	CO(NOC6H5
1	HENTSCHEL, /. prakt. Chem., 1887, 36, 310.
2	HOCHST FARB. W., D.R.P. 34607.
3	N. MELNIKOV and VINOKUROV, /. Obscei Khim., Ser. A., 1932, 64, 484.
4	D.R.P. 109933/1898.
6	N. MELNIKOV, /. prakt. Chem., 1930, 128, 233.