Chloral or Trichloroacetaldehyde

CHLORAL or TRICHLOROACETALDEHYDE, first prepared by J. von Liebig in 1832, is a heavy, oily and colourless liquid, of specific gravity 1.541 at 0°C, boiling point 97.7°C and the formula It has a greasy, somewhat bitter taste, and gives off a vapour at ordinary temperature which has a pungent odour and an irritating effect on the eyes. The word chloral is derived from the first syllables of chlorine and alcohol, the names of the substances employed for its preparation. Chloral is soluble in alcohol and ether, in less than its own weight of water, and in four times its weight of chloroform. It deliquesces in the air, and is converted by water into a hydrate, with evolution of heat ; it combines with alcohols and mercaptans. With an alkali, chloral gives chloroform (q.v.) and a formate; oxidizing agents give tri chloroacetic acid, When kept for some days, as also when placed in contact with sulphuric acid or a very small quantity of water, chloral undergoes spontaneous change into the poly meride metachloral a white substance slowly volatile in the air, and reconverted into chloral without melting at 180°C.

Chloral is prepared by passing dry chlorine into cooled absolute alcohol; towards the end of the operation the liquid is heated nearly to boiling. The alcohol is converted finally into a syrupy fluid, from which chloral is procured by treatment with sulphuric acid (P. Fritsch, 1894) . The crude chloral is distilled over lime, and is purified by further treatment with sulphuric acid, and by redistillation. A mixture of starch or sugar with manganese perox ide and hydrochloric acid may be employed instead of alcohol and chlorine (A. Staedeler, 1847).

Chloral hydrate, forms oblique rhombic prisms, perfectly transparent and only slightly odorous. The melting point of pure chloral hydrate is 57°, the boiling point 96-98°C. When heated with sulphuric acid it is converted into anhydrous chloral and chloralide, When mixed with water, chloral hydrate causes a considerable degree of cold ; and, as with camphor, small fragments of it placed on the surface of water exhibit gyratory movements. Chloral hydrate does not restore the colour to a solu tion of fuchsine decolorized by sulphurous acid; this absence of aldehydic property indicates that the water present is combined in the molecular condition. Chloral may be estimated by distilling the hydrate with milk of lime and measuring the volume of chloro form produced, or by hydrolysis with a known volume of standard alkali and back titration with standard acid. Chloral hydrate has the property of checking the decomposition of many albuminous substances, such as milk and meat; and a mixture with glycerin, according to J. Personne, is suitable for the preservation of anatomical preparations.

Pharmacology

and Therapeutics.—The alkaline hydrolysis (q.v.) of chloral hydrate, with production of chloroform and for mates, led Liebreich to the conjecture that a similar decomposi tion might be produced in the blood; and hence his introduction of the drug in 1869, as an anaesthetic and hypnotic. It is now known, however, that the drug circulates in the blood unchanged, and is excreted as urochloralic acid. The dose is often given in the form of the pharmacopoeial Syrupus Chloral, which contains ten grains of chloral hydrate to the fluid drachm. In large doses chloral hydrate is a depressant to the circulation and the respira tion, and also lowers the temperature. In the above dosage the drug is a powerful and safe hypnotic, acting directly on the brain, and producing no preliminary stage of excitement. About 20 min utes after taking such a dose, the patient falls into a refreshing sleep which, lasting several hours, is not distinguishable from natu ral sleep and is without disagreeable after-symptoms. Chloral hydrate rapidly induces a depression of the anterior horns of grey matter in the spinal cord, and as strychnine poisoning is accompa nied by violent stimulation of these areas, chloral hydrate is a valuable antidote in such cases. It should not be hypodermically injected. Its disadvantages are that it is powerless when there is pain, resembling in this feature nearly all hypnotics except opium (morphine) and hyoscin. Its action on the spinal cord has been employed with success in cases of tetanus, whooping-cough, uri nary incontinence and strychnine poisoning. In the latter case 20 grains in "normal saline" solution may be directly injected into a subcutaneous vein, but not into the subcutaneous tissues.

Toxicology.

In cases of acute poisoning by chloral hydrate, the symptoms may be summarized as those of profound coma. The treatment is to give a stimulant emetic such as mustard; to keep up the temperature by hot bottles, etc. ; to prevent or disturb the patient's morbid sleep by the injection of hot strong coffee into the rectum, and by shouting, flipping with towels, etc. ; to use arti ficial respiration in extreme cases. Strychnine injections are much less likely to save life after poisoning by chloral hydrate, than chloral hydrate is to save life in poisoning by strychnine.

Habitual use of chloral as a drug results in chronic poisoning. The victim is usually excited, loquacious, easily fatigued and suf fers from attacks of readily induced syncope. The patient may succumb to a dose only slightly larger than usual. There is no spe cific remedy; the patient must be persuaded to put himself under restraint, and the drug must be stopped at once and entirely.