Isothiocyanallyl, allyl mustard oil or commonly mustard oil, constitutes the bulk of the volatile oil of mustard. It has also been obtained from the following plants: Alliaria officinalis, Capsella Bursa pastoris, species of Cardamine and Sisymbrium, Cochlearia Armoracia and Thlaspi arvense.

1) Report of Schimmel & Co. April 1909, 55. 2) Apotheker Ztg. 17 (1902), 339.

Neither in the mustard seed nor in the other plants mentioned does the mustard oil occur as such but in the form of a glucoside known as sinigrin (myronate of potassium), which in the presence of the ferment myrosin and water, is hydrolized to mustard oil, d-glucose and potassium acid sulphate:

C10H16NS2KO9 + H20 = CSNC3H5 + C6H1206 + KHSO,.

However, side reactions also take place which account for the presence of cyanallyl and carbon disulphide, two substances that are never completely wanting in natural mustard oil.

Above 70° myrosin is decomposed and becomes inactive as ferment. At a temperature of 0° traces of rhodan allyl, CNSC3 H5,1) isomeric with allyl mustard oil, are also formed. Of interest is also the observation made by Guignard'2) that mustard oil is set free when the plants are subjected to the vapors of mercury, carbon disulphide or anaesthetics.

Chemically, mustard oil is obtained by the distillation of allyl-iodide or allylbromide with an alcoholic solution of potassium rhodanate, or by the dry distillation of this salt with the equivalent amount of a salt of allylsulphuric acid. Under the influence of the heat an inversion of this cyanate or rhodanate group to the Isothiocynate group takes place.

Isothiocyan allyl is a colorless oil which gradually turns yellow. It is optically inactive and possesses a very penetrating odor causing the flow of tears. Applied to the skin, it produces a burning sensation and causes blistering. The vapors are particularly harmful to the lungs. It is soluble in 8 vol. of 70 p. c. alcohol and is miscible in all proportions with 90 p. c. alcohol, likewise with ether, amyl alcohol, chloroform, benzene and petroleum ether. In water it is but sparingly soluble.

B. p. 150,7° (728,9mm.); d10.lo 1,0173.8)

According to observations made on technical products in the laboratory of Schimmel & Co., synthetic mustard oil possesses the following properties:

B. p. (the bulk of the oil) 151 to 153° (760 mm.), 30,2° (5 mm.); d15o 1,020 to 1,025; nD20o1,527 to 1,530.

1) E. Schmidt, Berl. Berichte 10 (1877), 187.

2) Compt. rend. U9 (1909), 91.

3) Kopp, Liebig's Annalen 98 (1856), 375.

When small amounts of mustard oil are mixed with twice their volume of concentrated sulphuric acid a violent evolution of carbon oxysulphide1) and sulphur dioxide2) takes place and allyl-amine sulphate, C3H5NH2H2S04, is formed. This remains in the test tube as a clear, slightly colored liquid, or occasionally congeals. As an unsaturated compound, mustard oil adds bromine with the formation of an oily dibromide, CSN-C3H5Br2, which is volatile with water vapors.

For the identification of mustard oil, allylthiourea (thiosin/NHC3H5 amine), CS<^ , is particularly suited. It crystallizes in

NH2 rhombic prisms that melt at 74°, has a faint leek-like odor and taste, and is readily soluble in water, alcohol and ether. The compound results when an excess of ammonia and some alcohol are added to mustard oil. The reaction is accelerated by gentle heat. For the quantitative determination of mustard oil, see the chapter on "The examination of volatile oils".

Exposed to light, mustard oil gradually acquires a reddish-brown color and the bottle is coated with a dirty orange-yellow film containing carbon, nitrogen, hydrogen and sulphur.

Prolonged contact with water or with heavy metals, such as copper, silver, tin, mercury, causes decomposition of the mustard oil with formation of cyanallyl. The metals combine with the sulphur to sulphides. Ethyl alcohol also gradually causes a change forming a partially sulphuretted allylurethane:

/NHQH, CSN • C3 H5 + C2 H5 OH = CS

OC2H5 It is because of this reaction that spirit of mustard gradually looses its therapeutic action.

The source of the carbon disulphide always found in mustard oil, even in the artificial product, has not yet been definitely ascertained. Experiments have shown3) that, whereas boiling of mustard oil with water in a flask connected with a reflux condenser for an hour does not yield carbon disulphide, appreciable amounts of this substance, together with carbon dioxide, are produced when mustard oil and water are heated in a sealed tube under pressure for several hours to a temperature of 100 to 105°. It may be assumed that in the nascent state mustard oil possesses a greater capacity for reaction and that under such conditions it reacts with water according to the following equation.

1) A. W. Hofmann, Berl. Berichte 1 (1868), 182. 2) Fluckiger, Arch, der Pharm. 196 (1871), 214. 3) Gadamer, Arch, der Pharm. 285 (1897), 53.

2CSNC3H5 + 2H20 = 2C3H5NH2 + C02 + CS2.

Carbon disulphide is also formed when mustard oil is allowed to remain in prolonged contact with water at ordinary temperature.

Of other mustard oils the following may be briefly described in.this connection.

Teothiocyanpropeny/, CSN • CH : CH • CH3. According to Pomeranz,1) traces of this occur in mustard oils. He assumes to have established its presence in artificial mustard oil by having identified acetic acid as well as formic acid among the oxidation products.

Secondary butyl mustard oil, CSN • CH(CH3) • CH2 • CH3, the isothiocyanate of secondary butyl alcohol, is the principal constituent of the oil of Cochlearia officinalis, and has been isolated from the oil of the herb of Cardamine amara. This mustard oil likewise does not occur as such, but in the form of a glucoside known as glucocochlearin.2)

Secondary butyl mustard oil is an optically active, colorless liquid possessing the characteristic odor of cochlearia oil.

B. p. 159,5°; d12o0,944.3)

Heated with ammonia to 100° it yields a thiourea which melts at 135 to 136° and which is optically active. In alcoholic solution, the oil gradually looses its original pungency. Presumably a partially sulphuretted urea is formed as in the case of allyl mustard oil.

The commercial "artificial oil of spoon wort" is isobutyl mustard oil, CSN • CH2 • CH • (CH3)2, hence not identical with the natural product. It boils at 162° and yields a thiourea melting at 93,5°.

1) Liebig's Annalen 351 (1907), 354.

2) Ter Meulen, Recueil des trav. chim. des P.-B. 24 (1905), 444. According to Chem. Zentralbl. 1905, II. 1255.

3) A. W. Hofmann, Berl. Berichte 7 (1874), 513.

Crotonyl mustard oil, CSNCH2CH2CH :CH2, is contained in a rape seed (Brassica Napus), likewise in the form of a glucoside.1). It is obtained when the seeds are mashed with white mustard which is rich in myrosin and subjecting the mixture to steam distillation. Ter Meulen2) succeeded in isolating the glucoside gluconapin though not in absolutely pure condition.

Crotonyl mustard oil is a colorless, strongly refractive liquid, the odor of which reminds of horse-raddish and allyl mustard oil. B. p. 174° with slight decomposition; d 10o/4o 0,933. With alcoholic ammonia the thiourea is obtained in fine needles that melt at 64°.

Attention was first directed to the presence of crotonyl mustard oil in rape seed because of the observation of poisoning in cattle fed on rape seed presscake. The natural mustard oil, however, is not identical with the artificial crotonyl mustard oils prepared by Hofmann3) and Charon,4) but only isomeric.

Benzyl mustard oil, CSNCH2C6H5, results upon the hydrolysis, produced by ferments, of the glucoside glucotropasolin, C14H18KNS209 + xH20, contained in Tropaeolum ma/us, and which probably also occurs in the ordinary cress, Lepidium sativum.5) It has the pungant odor of cress, and with ammonia orms a thiourea melting at 162°.

Phenylethyl mustard oil, CSNC2H4C6H6, constitutes the principal constituent of the oil from mignonette root. It is a liquid the odor of which reminds of horse-reddish. The thiourea melts at 137°.

V-Hydroxybenzyl mustard oil, C6H4OH(1)CH2NCS(4). The glucoside sinalbin, C30H12N2S2O15, which occurs in white mustard seed, yields upon the action of myrosin, the above mustard oil together with (d-glucose and sinapine bisulphate. Only traces of this sinalbin mustard oil are volatile with water vapor. Hence the water with which white mustard has been triturated, has a pungent taste but is wellnigh odorless.

1) Sjollema, Recueil des trav. chim. des P.-B. 20 (1901), 237. According to Chem. Zentralbl. 1901, II. 299.

2) Recueil des trav. chim. des P.-B 24 (1905), 444. According to Chem. Zentralbl. 1905, II. 1255.

3) Berl. Berichte 7 (1874), 514.

4) Annal. Chim. Physiol.VII. 17,262. According to Chem. Zentralbl. 1901, II. 300.

5) Gadamer, Arch, der Pharm. 237 (1899), 510; Berl. Berichte 32 (1899), 2338.