which are readily hydrolysed to give the following three substances :
Cl—CH=CH-AsCl2
(Cl—CH=CH)2AsCl
(Cl-CH=CH)3As
chloro vinyl
dichloro vinyl
trichlorovinyl
dichloroarsine
chloroarsine
arsine
In this mixture trichlorovinyl arsine always predominates and this substance has only a minor interest as a war gas, for its toxicity is low. Chlorovinyl dichloroarsine, which, besides its irritant action on the respiratory passages, also has a vesicant action similar to that of dichloroethyl sulphide, is of much greater importance. The resemblance in the properties of these two substances has been attributed to the presence of the two similar groups :
Cl—CH2—CHa— and Cl—CH=CH—.
Later, various other compounds were prepared and examined for possible employment as war gases. These are similar in constitution to the chlorovinyl arsines and are prepared similarly :
/3 Bromovinyl dibromoarsine (b.p. 140° to 143° C. at 16 mm. mercury pressure) was prepared by Lewis and Stiegler 1 by the action of acetylene on arsenic bromide mixed with aluminium chloride :
/Br
CH=CH + AsBr3 = Br-CH=CH-As( NBr
]8 Chlorostyryl dichloroarsine (b.p. 108° to 110° C. at 12 mm.) was obtained by Hunt and Turner 2 by acting on arsenic trichloride with phenylacetylene :
/Cl
Cl
j3 Chlorovinyl methyl chloroarsine (b.p. 112° to 115° C. at 10 mm. mercury pressure) was obtained by Das Gupta,3 by the action of acetylene on methyl dichloroarsine (see p. 278) in the presence of anhydrous aluminium chloride :
/Cl CH3-As(
NCH=CH-C1
1 LEWIS and STIEGLER, /. Am. Chem. Soc., 1925, 47,2546. 8 A. HUNT and E. TURNER, /. Chem. Soc., 1925, 127, 996. 3 DAS GUPTA, /. Ind> Chem. Soc., 1936, 13, 305.
286 ARSENIC COMPOUNDS
Phenyl ft chlorovinyl chloroarsine (b.p. 140° to 150° C. at 10 mm. mercury pressure) was obtained by the reaction of acetylene with phenyl dichloroarsine in the presence of aluminium chloride :
/Cl
Cl-CH=CH-As<
X
All these compounds, like the chlorovinyl arsines, are oily substances, somewhat yellow in colour, with extremely unpleasant odours. Their aggressive properties are still rather indefinite with the exception of /? chlorovinyl methyl chloroarsine, which does not irritate the nasal tissues like the chlorovinyl arsines, but produces blisters on the skin which heal only with difficulty.
Several compounds obtained by the action of ethylene on arsenic trichloride have also been prepared. Such, for example, is y8 chloroethyl dichloroarsine 1 :
/Cl
C1-CH2—CH2-As( XC1
This is a liquid with a boiling point of 93° to 94° C. at a pressure of 16 mm. of mercury which is both irritant and vesicant in its action. In the liquid condition, it penetrates linen and rubber ; in the vapour state, at concentrations which can be obtained in practice, it has no action on the human skin.2
PREPARATION OF THE CHLOROVINYL ARSINES
The mixture of the three chlorovinyl arsines is obtained, as indicated above, by the action of acetylene on arsenic trichloride.
/? Chlorovinyl dichloroarsine may also be obtained by the reduction of a hot solution of ft chlorovinyl arsenic acid which has been acidified with hydrochloric acid, by means of sulphur dioxide, hydriodic acid being employed as a catalyst.3 Another method of preparation is to heat a mixture of arsenic trichloride and trichlorovinyl arsine in a closed tube at 220° C. for 4 hours. The following reaction takes place 4 :
(ClCH=CH)3As + 2AsCl3 -> 3C1CH = CHAsCl2.
LABORATORY
PREPARATION
In
the
laboratory,
the
preparation
of the chlorovinyl arsines
may
be
carried out
by
condensing
arsenic trichloride with
1 RENSHAW and
WARE,
/. Am. Chem. Soc., 1925, 47, 2991 ; SCHERLIN and
EPSTEIN, Ber., 1928, 61, 1821 ;
NEKRASSOV, Her., 1928, 61, 1816.
2
FERRAROLO, Minerva Medico,, 1935 (II), 37, 30.
•
GIBSON and JOHNSON, /. Chem. Soc., 1931, 753.
4
GREEN
and PRICE, /. Chem. Soc., 1921, 119, 448.
CHLOROVINYL ARSINES: PREPARATION 287
acetylene in presence of aluminium chloride. The apparatus used is shown in Fig. 17. 45 gm. arsenic trichloride are placed in the vessel A, together with 15 gm. anhydrous aluminium chloride. While stirring and cooling with water, 6-8 litres of acetylene, which have been passed first through a sulphuric acid washbottle and then through a calcium chloride column C, are bubbled in. The reaction is accompanied by the evolution of heat, and the mixture should be cooled in order to maintain the temperature between 30° and 35° C. When the acetylene has been added, the reaction mixture is poured slowly into 200 ml. hydrochloric
FIG. 17.
acid cooled to about o° C. An oily layer forms and this is separated and fractionally distilled at reduced pressure (20-30 mm.). The arsenic trichloride which has not reacted distils first and then the chlorovinyl arsines as follows :
First fraction . Second fraction . Third fraction .
90° to 105° C. chlorovinyl dichloroarsine. 125° to 140° C. dichlorovinyl chloroarsine. 145° to 160° C. trichlorovinyl arsine.
Preparation of Chlorovinyl Dichloroarsine and Dichlorovinyl Chloroarsine from Trichlorovinyl Arsine.1 80 gm. trichlorovinyl arsine and 66-2 gm. arsenic trichloride are placed in a thick-walled glass tube which is then sealed in the flame. The tube is placed in an outer tube of steel, covered with asbestos, and the whole heated for 4 hours at 220° to 250° C. After allowing to cool, the glass tube is opened at the end and the oily contents distilled under reduced pressure. The products obtained are as follows :
56 gm. chlorovinyl dichloroarsine.
80 gm. dichlorovinyl chloroarsine.
1 GREEN and PRICE, /. Chem. Soc., 1921, 119, 448.
288 ARSENIC COMPOUNDS
INDUSTRIAL MANUFACTURE
The process used in America for the manufacture of the chlorovinyl arsines may be summarised as follows 1 :
6-3 kgm. arsenic trichloride and 1-16 kgm. aluminium chloride are placed in a 2-gallon enamelled autoclave, and while they are continually stirred, a current of acetylene which has been dried with sulphuric acid and calcium chloride is bubbled in. The quantity of acetylene used is measured by means of a rotary gas-meter; it is in equimolecular amount with the arsenic trichloride. During this operation the temperature slowly rises
from
25° to 30° C. initially to 40° to 45° C., but it should in any
case
be kept below 60° C. When all the acetylene has been
absorbed (about 2 hours) the product is separated by washing first with 20% hydrochloric acid, which extracts the arsenic chloride, and distilling the residue. This is carried out in a special cast-iron still of about i gallon capacity. The distillate is then fractionally distilled once more under reduced pressure to separate the three chlorovinyl arsines.
PHYSICAL AND CHEMICAL PROPERTIES
The three chlorovinyl arsines are colourless liquids at ordinary temperatures and, if pure, are stable. In presence of small quantities of arsenic trichloride, however, they become violet or brown in time, and the speed of this change as well as the final colour seems to depend on the quantity of arsenic chloride present.
They have high boiling points (190° to 260° C.), but on heating at ordinarypressure easily decompose. Chlorovinyl dichloroarsine is thus decomposed into dichlorovinyl chloroarsine and arsenic trichloride, dichlorovinyl chloroarsine into chlorovinyl dichloroarsine and acetylene, etc. This behaviour supports the belief that an equilibrium exists between the three chlorovinyl arsines and their components, acetylene and arsenic trichloride. The hypothesis is confirmed by the observation that from the reaction between acetylene and arsenic trichloride, it is not possible to produce any one of these compounds solely; a mixture of all three is always obtained.
They are sparingly soluble in cold water or in dilute acids, but all—except trichlorovinyl arsine, which is insoluble in alcohol— dissolve readily in alcohol, benzene, kerosene, olive oil, petrol and other organic solvents.
1 Detailed accounts of the best conditions for carrying out the reactions may be found in Ind. Eng. Chem., 1923, 15, 290.
CHLOROVINYL DICHLOROARSINE
289
Chemically, they are unsaturated and unstable compounds. As Conant * has pointed out, they all have a chlorine atom attached to that carbon of the vinyl group which is not adjacent to the arsenic atom. The following are therefore their correct names:
ft chlorovinyl dichloroarsine. /J/J' dichlorovinyl chloroarsine.
trichlorovinyl arsine.
(a) j3 Chlorovinyl dichloroarsine
(M.Wt. 207-3)
I
Cl—CH = CH—As<
PHYSICAL PROPERTIES
Chlorovinyl dichloroarsine when pure is a colourless liquid which boils at ordinary pressures at 190° C., with decomposition. At reduced pressure, however, it distils unchanged at the following temperatures :
MM. PRESSURE
B.P. ° C.
30
96-98 (Lewis and Perkins)
24
93-94 (Burton and Gibson) 2
15
79 (Lewis and Perkins)
12
77-78 (Wieland)
10
76 (Gibson and Johnson) 3
10
72 (Lewis and Perkins)
The melting point is -f 0-1° C.
according
to
Gibson and
Johnson, — 13° C. according to
Nekrassov,
and
— 18-2° C.
according to Libermann.
The odour of this substance recalls that of geraniums and is perceptible even at a dilution of 14 mgm.per cu. m. of air (Prentiss).
In the following table the specific gravity and corresponding specific volume are given at various temperatures :
Temperature (° C.)
S.G.
Specific Volume
O
1-9200
0-5232
10
1-9027
0-5255
15
1-8940
0-5279
20
1-8855
0-5302
25
1-8768
0-5328
30
1-8682
0-5352
40
I-85I3
0-5401
50
I-8338
0-5453
60
1-8164
0-5505
1 Chemical Warfare Communications, Offense Research Section of the U.S. Chemical Warfare Service (seeInd. Eng. Chem., 1923, 15, 290).
1 BURTON and GIBSON, /. Chem. Soc., 1926, 464.
8 GIBSON and JOHNSON, /. Chem. Soc., 1931, 754.
WAR GASES.
20.0ARSENIC COMPOUNDS
The vapour tension of /J chlorovinyl dichloroarsine at temperature t may be calculated from the formula (see p. 5).
i . 2781.69 log p = 9-123-2^T7
In the following table are given the values of the vapour tension at various temperatures :
Temperature
Vapour Tension
° C.
MM. MERCURY
o
0-087
10
0-196
20
0-394
30
0-769
40
1-467
50
2-679
75
9'66
100
32-50
150
175^0
175
487-6
Following are the values
of the volatility of ft chlorovinyl
dichloroarsine l:
° C.
MGM. PER CU. M.
O
I,OOO
20
2,300
40
I5,60O
The latent heat of vaporisation is 57-9, the mean coefficient of thermal expansion between o° C. and 50° C. is 0-00094 and the vapour density is 7-2.
It is readily soluble in benzene, absolute alcohol, olive oil, kerosene and other organic solvents. It is sparingly soluble in water (about 0-5 gm. in 1,000 ml.).2
CHEMICAL PROPERTIES
Owing to the unsaturated character of the molecule and the presence of two chlorine atoms attached to the arsenic atom, this substance is highly reactive.
Water. In contact with water, or with a damp atmosphere,3 /j chlorovinyl dichloroarsine is rapidly decomposed even at ordinary temperatures, the following reaction taking place :
/Cl
H\
Cl-CH=CH-As<XC1
+
W >0 = 2 HC1 + Cl-CH=CH-As-O
1 SHIVER, /. Chem. Education, 1930, 7, 108 ; VEDDER, The Medical Aspects of
Chemical Warfare, Baltimore, 1925.
8
S. NAMETKIN and W. NEKRASSOV, Z. anal. Chem., 1929, 77, 285.
*
LEWIS and PERKINS, Ind. Eng. Chem., 1923, 15, 290.
p CHLOROVINYL DICHLOROARSINE
291
The degree of hydrolysis is notably increased by an increase in the temperature. The chlorovinyl arsenious oxide formed is a white, crystalline powder, sparingly soluble in water, alcohol and carbon disulphide and melting at 143° C. This oxide is also formed on treating /J chlorovinyl dichloroarsine with aqueous ammonia solution :
ClCH=CHAsCl2 + NH4OH = ClCH=CHAsO + NH4C1 + HC1.
Alkalies. Alkalies completely decompose the molecule. Green and Price x have shown that on adding even very dilute cold solutions of sodium hydroxide or carbonate, chlorovinyl arsenious oxide is never obtained, but acetylene and arsenious acid, as follows:
/Cl
Cl-CH=CH-As(
+ 6 NaOH = Na3AsO3 + 3 Nad + C2H2 4- 3 Hj
XC1
When a 15% sodium hydroxide solution is employed at
temperatures
below 37° C., this decomposition takes place
quantitatively, and only in the case of/? chlorovinyl dichloroarsine.
This fact may be
used for
the quantitative
determination of
/J chlorovinyl dichloroarsine
in presence of dichlorovinyl chloro-
arsine and trichlorovinyl arsine (Lewis).
Halogens. The
halogens
readily react
with chlorovinyl
dichloroarsine. Thus on adding a dilute solution of bromine in carbon tetrachloride to a solution of /3 chlorovinyl dichloroarsine in the same solvent, the colour of the bromine gradually disappears while small lamellae of a bromo-derivative separate. This melts at 122° C., and its formation has been suggested by Green and Price as a means of detecting chlorovinyl dichloroarsine.2
Nitric Acid. Chlorovinyl dichloroarsine, when treated with nitric acid, is oxidised to /? chlorovinyl arsenic acid 3
/OH
Cl-CH=CH-As4=0
\OH
If concentrated nitric acid is employed, this oxidation is very violent and it is necessary to cool the reaction mixture. On the other hand, when dilute nitric acid is employed it is necessary to warm it in order to carry out the reaction. On standing, a colourless crystalline mass separates; this is ;8 chlorovinyl arsenic acid which may be purified by recrystallisation from a
1 GREEN and PRICE, /. Chem. Soc., 1921, 119, 448. 2 GREEN and PRICE, loc. cit.
8 MANN and POPE, J. Chem. Soc., 1922, 121, 1754.
292 ARSENIC COMPOUNDS
mixture of acetone and carbon tetrachloride. It forms needles, melts at 130° C. and is soluble in water and alcohol.
On warming this acid with a concentrated sodium hydroxide solution it is completely decomposed into acetylene, arsenic acid and hydrochloric acid :
When it is heated in vacua to 110° to 115° C., the acid loses a molecule of water and forms the corresponding anhydride :
Cl-CH=CH-As
This anhydride is a white hygroscopic powder which decomposes violently at 242° C.
Hydrogen Peroxide. Chlorovinyl dichloroarsine reacts with
hydrogen peroxide forming chlorovinyl arsenic acid, as with nitric acid 1:
Cl-CH=CH-AsCl2+ 2 H2O2 =
/OH
= Cl-CH=CH-AsfO +2HC1 + O
\OH
Potassium Iodide. Potassium iodide reacts with j8 chlorovinyl dichloroarsine with evolution of heat and formation of j8 chlorovinyl diiodoarsine :
C1-CH=CH-As(
NI
This iodo-derivative forms yellowish-brown crystals, m.p. 37'5° to 38-5° C. It is sparingly soluble in ligroin, but readily in alcohol and benzene.2
Hydrogen Sulphide. By the action of hydrogen sulphide on /? chlorovinyl dichloroarsine in alcohol solution, the corresponding sulphide,3 C1CH = CHAsS, is formed. When pure, this forms a plastic mass insoluble in the usual organic solvents except carbon disulphide. It has a strong irritant action on the organism.* A method of detecting chlorovinyl dichloroarsine is based on the formation of this sulphide 5 (see p. 328).
1 WIELAND, Ann,, 1923, 431, 38.
2
W. LEWIS and H. STIEGLER, /. Am. Chem. Soc., 1925, 47, 2551.
8
KRETOV and coll., /. Obscei Khim., Ser. A, 1931, 1, 411.
•
LEWIS and STIEGLER, he. cit.
1 S. NAMETKIN and W. NEKRASSOV, Z. anal. Chem., 1929, 77, 285
0)8' DICHLOROVINYL CHLOROARSINE
293
Diphenylamine. Chlorovinyl dichloroarsine reacts on heating with diphenylamine to form 10 chloro 5-10 dihydro phenarsazine1:
in canary-yellow crystals with melting point 191° to 193° C. (see p. 323). Pure /? chlorovinyl dichloroarsine when kept in glass vessels is stable at ordinary temperatures, particularly in absence of light, while in presence of iron it is slowly converted into dichlorovinyl chloroarsine and trichlorovinyl arsine.
It does not attack steel appreciably and when stored in projectiles causes only a slight superficial rusting of the metal walls. However, it attacks lead slightly and is itself partially decomposed.
j8 Chlorovinyl dichloroarsine has an irritant action on the eyes and on the respiratory tract. The minimum concentration causing irritation is 0-8 mgm. per cu. m. of air ; that is to say, less than can be detected by odouT (Prentiss). The fatal concentration, according to Vedder, is 48 mgm. per cu. m. for 30 minutes' respiration. It also has a considerable vesicant action when allowed to remain in contact with the skin for a time.a
The lethal index is 1,500 according to Muller, and 1,200 for
10 minutes' exposure according to Prentiss.
(b) /3]8' Dichlorovinyl Chloroarsine
(M.Wt. 233-3)
Cl—CH=CHV
>As—Cl
Cl—CH=CH/
PHYSICAL PROPERTIES
When pure, $8' dichlorovinyl chloroarsine is a clear transparent liquid of a yellow or yellowish-brown colour. It boils at ordinary pressure at 230° C. with decomposition. The boiling points at reduced pressures are as follows 3:
MM. MERCURY
° C.
II
113
15
H9
3«
136
The specific gravity at 20° C. is 1702, and the vapour density 8-1.
1 MILLER and coll., /. Am. Chem. Soc., 1930, 52, 4164; GIBSON, /. Am.
Chem. Soc., 1931, 53, 376.
1 H. BUSCHER, Grunund Gelb-kreuz,Hamburg, 1932, 150.
* LEWIS and PERKINS, he. cit. ; WIELAND, he. cit. ; GRYSZKIEWICZ and coll.,
Butt. soc. chim., 1927, 41, 1750.
294 ARSENIC COMPOUNDS
The vapour tension of /J/?' dichlorovinyl chloroarsine may be calculated at any temperature t from the formula (see p. 5).
3295-3
log p = 9.983 —
273 + t
This substance is insoluble in dilute acids, but dissolves readily in alcohol and the common organic solvents.
CHEMICAL PROPERTIES
Like the preceding compound, this also shows great chemical reactivity owing to the unsaturated character of the molecule :
Water. Water hydrolyses it even at ordinary temperatures (Lewis and Perkins), the corresponding oxide being formed :
2(C1CH = CH)2AsCl + H20 = (C1CH = CH)2As2O +2HC1. This forms crystals melting at 62° to 63° C., insoluble in water,
sparingly soluble in cold alcohol, but
soluble in hot alcohol, and
in ether.
Alkalies. The alkalies decompose
dichlorovinyl chloroarsine
completely, forming acetylene and arsenious acid. This reaction, unlike the corresponding one with chlorovinyl dichloroarsine, takes place only above 37° C. and is never quantitative.1
Nitric Acid. By the action of concentrated nitric acid on j3]8' dichlorovinyl chloroarsine a crystalline product is obtained which melts at 97°to 99° C.; this is the nitrate of $3' dichlorovinyl arsenic acid2: (ClCH=CH)aAsOOH.HNO3. This compound apparently does not ionise in solution, but when dissolved in aqueous alcohol and treated with sodium hydroxide solution until the nitric acid is neutralised, decomposition takes place. On extracting with chloroform and evaporating the extract, a crystalline mass remains which consists of dichlorovinyl arsenic acid (Mann and Pope), (CHCl=CH)2AsOOH. This is purified by recrystallisation from water or carbon tetrachloride, when it melts at 120° to 122° C. Like cacodylic acid, it is amphoteric, forming salts with acids as well as with bases.
According to Green and Price this reaction with nitric acid may be employed very conveniently for the identification of dichlorovinyl chloroarsine.
Hydrogen Peroxide. This arsine also is vigorously oxidised by hydrogen peroxide (Wieland). After evaporating the solution, dichlorovinyl chloroarsine remains as an oil which solidifies after
1 LEWIS and PERKINS, loc. cit. * MANN and POPE, loc.cit.
