Sartori The War Gases Chemistry and analysis

134 AROMATIC ESTERS

Alcoholic ammonia reacts with benzyl bromide, even in the cold, to form tribenzylamine l (C6H5CH2)3N.

Benzyl bromide, when treated with an alcoholic solution of silver acetate, separates silver bromide rapidly, even in the cold (Kekule").

In contact with iron it decomposes in a short time. Because of this decomposition it must be placed in lead containers if it is to be used in projectiles.2

During the war a mixture of benzyl bromide, castor oil, alcohol, sodium thiosulphate and glycerol was employed.3

This substance, which has well-known lachrymatory properties, may be obtained according to Cannizzaro4 by the action of phosphorus iodide with benzyl alcohol or by the action of potassium iodide on benzyl chloride or bromide.

According to some authors, benzyl iodide was used as a war gas by the French in March, 1915.

LABORATORY PREPARATION 5

150 ml. 95% ethyl alcohol, 20 gm. benzyl bromide and 25 gm. potassium iodide are placed in a flask of 250-300 ml. capacity fitted with a reflux condenser. This is then warmed on the water-bath to 50° to 60° C. with continual agitation. After heating for half an hour, the product is poured into 150 ml. water, the oily layer separated, washed with water and crystallised by means of a freezing mixture. The crystals are collected and purified by crystallisation from alcohol.

PHYSICAL AND CHEMICAL PROPERTIES

Benzyl iodide forms colourless crystals melting at 24-1° C. The liquid has a specific gravity of 17735 at 25° C. and boils with decomposition at 226° C. (Lieben).6 The vapour density is 7-5. It is insoluble in water, soluble in alcohol, ether and benzene and slightly soluble in carbon disulphide (Kumpf).

Benzyl iodide has a volatility of 1,200 mgm. per cu. m. of air.

KEKULE, Ann,, 1866, 137, 190.

ALEXEJEVSKY and coll., /. Prikl. Khim., 1928, 1, 194.

S. DE STACKELBERG, Le piril chimique et la croix violette, Lucerne, 1929. CANNIZZARO, Gtnelins Handbuch, 6, 38.

MEYER, Ber., 1877, 10, 311 ; KUMPF, Ann., 1884, 224, 126. LIEBEN, Jahresber. Fortschr. Chem., 1869, 425.

Like the two previous compounds, it is decomposed by water with difficulty.1

Crystals of benzyl iodide when gently heated become red in colour owing to incipient decomposition. By the action of silver acetate in presence of acetic acid, silver iodide and benzyl acetate are formed (Lieben).

It reacts easily with tertiary amines, forming quaternary ammonium iodides.2

It may be classed among the strongest lachrymators. The lower limit of irritation is 2 mgm. per cu. m. of air (Miiller). The maximum concentration which a normal man can support for a period of not more than i minute is 25-30 mgm. per cu. m.

/CH2C1

C6H/ \N02

Ortho-nitrobenzyl chloride was prepared in 1883 by Abelli,3 together with the meta-compound, by the reaction of concentrated nitric acid on benzyl chloride. It may also be obtained, according to Haussermann and Beek,4 by the action of chlorine at 130° to 140° C. on a mixture of 2 parts of o-nitrotoluene and i part sulphur.

According to Lindemann,5 it was used by the French during the war mixed with ^-nitro benzyl chloride under the name of " Cedenite."

PHYSICAL AND CHEMICAL PROPERTIES

o-Nitrobenzyl chloride forms crystals with a melting point of 48° to 49° C. It is purified by crystallisation from ligroin. Its vapour density is 5-9. It is insoluble in water, but easily soluble in cold benzene and in ether and alcohol on warming.

With potassium iodide it is easily converted into o-nitrobenzyl iodide,6 and an alcoholic solution of potassium cyanide converts it into o-nitrobenzyl cyanide.7 Potassium permanganate oxidises it to o-nitrobenzoic acid.

The lower limit of irritation is 1-8 mgm. per cu. m. of air (Lindemann). It has a vesicant action.

1 P. RONA, Z. ges. exp. Med., 1921, 13, 16.

its use was abandoned towards the end of the war because of the ease with which it was dealt with by the ordinary carbon niters and of the inconvenience caused by its attack on iron containers. It is also known as " T-Stoff."

Xylyl bromide may be easily prepared by the reaction of bromine on commercialxylol.2 This reaction is carried out either by heating the xylol to 115° C. or by exposing the reaction-mass to the action of a light source rich in ultra-violet radiations and keeping the temperature at 50° to 60° C.3

In both cases the following reaction takes place :

Since commercial xylol is a mixture of the three isomeric xylenes, ortho, meta and para, the method of bromination mentioned above produces a mixture of the three derivatives :

All these three compounds have lachrymatory properties.

In the bromination of xylol a secondary reaction also takes place; this is the conversion of xylyl bromide into xylylene bromide, due to the tendency of bromine to react with xylyl bromide as well as with the xylol also present.

Br2 =

1RADZISZEVSKY and WISPEK, Ber., 1882, 15, 1747.

2ATKINSON and THORPE, /. Chem. Soc., 1907, 91, 1695.

3SCHRAMM, Ber., 1885, 18, 1278 ; FARBENFABR, F. BAYER, D,R P

i38 AROMATIC ESTERS

reduced pressure. After the xylol had been recovered, the residue was employed without rectification or purification.

PHYSICAL AND CHEMICAL PROPERTIES

In the pure state it is a colourless liquid boiling between 210° and 220° C., with a density of 1-4, and has an aromatic odour, which when much diluted is reminiscent of elder blossom.

The volatility at o° C. is 140 mgm. per cu. m. of air, and at

20° C. is 600 mgm. per cu. m.

It is slowly decomposed by water, like benzyl iodide.1 The crude product energetically attacks iron and so must be stored in lead-lined containers.

The minimum concentration capable of provoking irritation is 1-8 mgm. per cu. m. The limit of insupportability is 15 mgm. per cu. m. The mortality-product is 6,000 according to Miiller. However, according to Prentiss it is 56,000.

Analysis of the Aromatic Esters

DETECTION

The aromatic esters are identified by saponifying them with alcoholic potash and then examining the product for the halogen hydroacids with silver nitrate solution.2

Detection of Benzyl Chloride. Benzyl chloride, on heating under reflux with a solution of lead nitrate, forms benzaldehyde which is easily recognised by its almond-like odour.

Another method of detecting benzyl chloride, according to Lob,3 consists in passing the vapour of the substance to be examined over a platinum wire heated to redness and then testing for hydrochloric acid in the product with silver nitrate.

Detection of Benzyl Bromide. According to Kekule",4 when benzyl bromide is treated with an alcoholic solution of silver acetate, a yellow precipitate of silver bromide rapidly separates even in the cold.

QUANTITATIVE DETERMINATION

The quantitative determination of the aromatic esters is best carried out by the same reactions given above for their detection.

Determination of Benzyl Chloride. Benzyl chloride may be determined, according to Schulze, in the following manner 6:

RONA, Z. ges. exp. Med., 1921, 13, 16.

WESTON, Carbon Compounds, London, 1927, 21.

LOB, Ber., 1903, 36, 3060.

KEKUL£, Ann., 1866, 137, 191.

K. SCHULZE, Ber., 1884, 17, 1675.

added and then the whole is heated to boiling for about 5 minutes. At the end of the reaction, the precipitate formed is filtered on a weighed Gooch crucible, washed first with alcohol, then with hot water slightly acidified with nitric acid and then again with alcohol. The crucible is heated, first gently, then to red heat and reweighed. From the gain in weight the quantity of benzyl chloride in the sample may be calculated.

Determination of Benzyl Bromide. The determination of this substance may be carried out by the method already described for benzyl chloride. However, according to Van der Laan,1 it is sometimes more convenient to decompose the substance directly with a measured volume of standardised alcoholic silver nitrate solution and to titrate the excess of the latter with ammonium thiocyanate solution by the Volhard method.

Determination of Benzyl Iodide. The following method may be employed for the quantitative determination of benzyl iodide :

About 2 gm. benzyl iodide are weighed into a flask and then 50 ml. 20% alcoholic potash solution are added and the mixture refluxed for about an hour. At the completion of the saponification the contents of the flask are allowed to cool and then transferred to a 5oo-ml. flask and made up to volume with water. 100 ml. of the resulting solution are placed in a distillation flask and distilled in steam after adding 10 gm. ferric ammonium alum and acidifying with sulphuric acid. By this treatment, the ferric salt is converted to the ferrous condition, liberating iodine which is distilled over into 5% potassium iodide solution. At the end of the distillation, the free iodine in the potassium iodide solution is titrated with a decinormal solution of sodium thiosulphate. From this, the amount of iodine and so the quantity of benzyl iodide in the sample may be calculated.

1 VANDERLAAN, Rec. trav. Chim., 26, 54.

ACROLEIN : PREPARATION 141

studies of Moureu 1 on this subject that it was possible to obtain higher yields. In his method a. mixture of 5 parts potassium bisulphate and I part potassium or sodium sulphate is used.

Little is known concerning the action of the acid sulphates on glycerol. A recent theory suggests that salts of glycero-sulphuric acid are first formed :

LABORATORY PREPARATION 2

100 gm. glycerol, 80 gm. potassium bisulphate and 20 gm. anhydrous sodium sulphate are placed in a flask A of about I litre capacity, which is fitted with a tap-funnel and connected by means of a glass tube (see Fig. 9) with another flask B of the

FIG. 9.

same size, this being also connected to a Liebig condenser. The first flask is immersed in an oil bath and heated to 160° to 180° C. The products of the reaction—water, acrolein, etc.—pass over

1 MOUREU, Compt. fend., 1919, 169, 621, 705, 885 and 1068 ; Bull. soc. Mm.,

1920, 27, 297.

8 NEKRASSOV, op cit. ; E. ZAPPI, Annies Asoc. Quint. Argentina, 1930, 18, 243.

142 ALDEHYDES

into the flask B in which i gm. hydroquinone has been placed. When the acrolein commences to distil, a further 100 gm. glycerol are slowly run into A from the tap-funnel and the reaction continued for 4-5 hours by heating to about 250° C. at the end. In the receiver B a liquid collects which separates into two layers ; the lower of these is an aqueous solution of acrolein and the upper a solution of water in acrolein. The upper layer is separated off, washed with soda solution, dried over fused calcium chloride and distilled.

It is advisable to add o-r-o-2 gm. hydroquinone in order to retard polymerisation.

INDUSTRIAL MANUFACTURE

The industrial manufacture of acrolein is carried out in cylindrical iron vessels of about 30 cm. diameter fitted with agitators and closed by a lid having three holes, through one of which the glycerol is introduced, through the second passes a thermometer and through the third a condenser leading to a large flask heated on a water-bath. This flask is also fitted with a thermometer and may be connected to another condenser, cooled by water.

In the iron vessel 2 kgm. potassium bisulphate and 400 gm. potassium sulphate are placed, while 600 gm. glycerol of 28° Be. are run in. The whole is then heated in an air-bath until the temperature inside the vessel reaches 100° C., when the reaction commences and a mixture of water and acrolein begins to distil. The temperatures in the first condenser and in the flask are then so regulated that the mixture of vapours enters the second condenser at a temperature of about 70° C. A considerable proportion of the water and compounds with higher boiling points is thus condensed in the flask while the acrolein, together with the remaining water vapour condenses in the second condenser and is collected in the appropriate receiver.

When only a little glycerol remains in the iron vessel, more is added at such a rate that the speed of distillation is not diminished.

The internal temperature should be maintained throughout the reaction at 195°C.

The crude acrolein obtained is dried over calcium chloride and redistilled. The yield is 60-65% of theoretical (Moureu).

PHYSICAL AND CHEMICAL PROPERTIES

In the pure state acrolein is a clear liquid boiling at 52°C. and solidifying at — 88° C. Its specific gravity is 0-86 at 15° C., and its vapour density is 1-94. Its volatility at 20° C. is 407,000 mgm.