Substances, colourless

The amino-acids are colourless, crystalline substances which melt with decomposition. They are mostly soluble in water and insoluble in alcohol. 

CH2CI2. A colourless liquid with a chloroform-like odour b.p. 4I°C. Prepared by heating chloroform with zinc, alcohol and hydrochloric acid manufactured by the direct chlorination of methane. Decomposed by water at 200°C to give methanoic and hydrochloric acids. Largely used as a solvent for polar and non-polar substances, particularly for paint removal (30%), dissolving cellulose acetate and degreasing (10%). It is more stable than carbon tetrachloride or chloroform especially towards moisture or alkali. It is somewhat toxic. U.S. production 1981 280000 tonnes. 

Colourless liquid b.p. 69 5 C. Manufactured from propanone by conversion to pinacone and passing its vapour over heated KHSO4. Slowly changes to a rubber-like substance the change is hastened by metallic sodium or peroxides. Used in the manufacture of artificial rubber. 

CH3COCH2CH1COCH3. Colourless liquid which becomes yellow on standing b.p. I9PC. Obtained by boiling 2,5-dimethylfuran with dilute sulphuric acid. It readily condenses with a variety of substances to give derivatives of furan, thiophen and pyrrole, and is a solvent for cellulose acetate. 

C(,Hi3N02, CH3 CH2-CHMe-CHNH2-COOH. Colourless crystals, m.p. 284 C (decomp.). The naturally occurring substance is dextrorotatory. An amino-acid, occurring with leucine as a product of protein hydroly-... 

L,2-propadiene, allene, CH2=C = CH2, CjH4. Colourless gas prepared by the electrolysis of potassium itaeonate, or by the action of zinc and alcohol on 1,3-dibromopropane. It is easily isomerized to propyne (methylacetyl-ene), and is produced as a mixture with this substance from some reactions. 

NH2-C0-NH NH2,CH5N30. Colourless crystalline substance m.p. 96" C. Prepared by the electrolytic reduction of nitrourea in 20% sulphuric acid at 10 "C. Forms crystalline salts with acids. Reacts with aldehydes and ketones to give semicarbazones. Used for the isolation and identification of aldehydes and ketones. 

H02C(CH2)2C02H. Colourless prisms m.p. 182 C, b.p. 235°C. Occurs in amber, algae, lichens, sugar cane, beets and other plants, and is formed during the fermentation of sugar, tartrates, malates and other substances by a variety of yeasts, moulds and bacteria. Manufactured by the catalytic reduction of maleic acid or by heating 1,2-dicyanoethane with acids or alkalis. Forms an anhydride when heated at 235°C. Forms both acid and neutral salts and esters. Used in the manufacture of succinic anhydride and of polyesters with polyols. 

Colourless crystals m.p. 174 C. It is obtained by the action of heat on phenyl salicylate. It may be reduced to xanthene. It is the parent substance of the xanthone group of dyestuffs. 

Aniline when freshly distilled is a colourless liquid of b.p. 184° and d, 1025 on exposure to air and light, it develops a deep brown colour. It is an extremely important substance technically, being the starting point of many azo and other dyes. 

Pure phenol is a colourless crystalline substance, having m.p. 43°, and b.p. 182° on exposure to air, it slowly sublimes, and on exposure to light, develops a pink colour. It has a characteristic odour, and a limited solubility in water. Phenol in dilute aqueous solution has strongly antiseptic properties, but the crystalline substance should not be allowed to come in contact with the skin, as it may cause severe blistering. 

The nitrosamines are insoluble in water, and the lower members are liquid at ordinary temperatures. The separation of an oily liquid when an aqueous solution of an amine salt is treated with sodium nitrite is therefore strong evidence that the amine is secondary. Diphenylnitrosoamine is selected as a preparation because it is a crystalline substance and is thus easier to manipulate on a small scale than one of the lower liquid members. For this preparation, a fairly pure (and therefore almost colourless) sample of diphenyl-amine should be used. Technical diphenylamine, which is almost black in colour, should not be employed. 

Filter at the pump, and wash well with water. (Yield, about 20 g.) Recrystallise a portion from hot methylated spirit, reserving the remainder for the following preparation. Benzoin is a very pale yellow (almost colourless) crystalline substance, m.p. 137°. 

Salicin is a colourless crystalline substance, soluble in water. It does not reduce Fehling s solution nor does it give a coloration with ferric chloride. On hydrolysis with emulsin, glucose and salicyl alcohol are produced the former reduces Fehling s solution and the latter gives a violet coloration with ferric chloride. 

The use of an indicator or marking substance, which is adsorbed on the column in a position in known relation to that of the colourless substance (e.g., Sudan III for isolation of Vitamin D upon alumina). 

Owing to the great tendency of hydrazobenzene to undergo oxidation, all operations involving filtration should be carried out as rapidly as possible and air should not be drawn through it unnecessarily. The substance should be dried in a vacuum desiccator it can only be preserved in a colourless condition if it is kept in an atmosphere of carbon dioxide or nitrogen or in sealed vessels. 

The following alternative procedure is recommended and it possesses the advantage that the same tube may be used for many sodium fusions. Support a Pyrex test tube (150 X 12 mm.) vertically in a clamp lined with asbestos cloth or with sheet cork. Place a cube (ca. 4 mm. side = 0 04 g.) of freshly cut sodium in the tube and heat the latter imtil the sodium vapour rises 4 5 cm. in the test-tube. Drop a small amount (about 0-05 g.) of the substance, preferably portionwise, directly into the sodium vapour CAUTION there may be a slight explosion) then heat the tube to redness for about 1 minute. Allow the test tube to cool, add 3-4 ml. of methyl alcohol to decompose any unreacted sodium, then halffill the tube with distilled water and boil gently for a few minutes. Filter and use the clear, colourless filtrate for the various tests detailed below. Keep the test-tube for sodium fusions it will usually become discoloured and should be cleaned from time to time with a little scouring powder. 

Aminoacridine hydrochloride monohydrate (Acramine yellow, Monacrin) [52417-22-8] M 248.7, m >355 , pKj 4.7, pKj 9.99. Recrystd from boiling H2O (charcoal Ig in 300 mL) to give pale yellow crystals with a neutral reaction. It is one of the most fluorescent substances known. At 1 1000 dilution in H2O it is pale yellow with only a faint fluorescence but at 1 100,000 dilution it is colourless with an intense blue fluorescence. [Albert and Ritchie Org Synth Coll Vol III 53 7955 Falk and Thomas Pharm J 153 158 1944.] See entry in Chapter 4 for the free base. 

Simple asphyxiant. Some gases and vapours present at high concentrations act as asphyxiants by reducing the oxygen content of air. Many of these are odourless and colourless. Many also pose a fire or explosion risk, often at values below which asphyxiation can occur. (Although capable of asphyxiation, they are not considered to be substances hazardous to health under COSHH.)... 

Base V, CjgHj or 26O2N2. This substance is present in small quantity (about 1-5 per cent.) in crude aphylline hydrochloride and when the base is liberated into ether from this salt, the solution deposits Base V on standing. It is sparingly soluble in ether or light petroleum, readily in benzene or alcohol and crystallises from benzene-light petroleum in colourless tablets, m.p. 137° (dec.). 

Oscine, CgHiaOjN, This substance, for which the name scopolin is in use in continental Europe, was first examined by Hesse and later t Luboldt. It forms colourless, hygroscopic prismatic crystals, m.p. 109 from ether or light petroleum, and boils at 241-3°. cZZ-Oscine has bee resolved into the d- and Z-forms by King by crystallisation of tl d-hydrogen tartrates. The characters of the three forms of oscine and ( their picrates and hydrochlorides are tabulated on p. 87. 

---