Odour general

Note cautiously the characteristic odour of acetaldehyde which this solution possesses. Then with the solution carry out the following general tests for aldehydes described on p. 341 Test No. I (SchiflF s reagent). No. 3 (Action of sodium hydroxide). No. 4 (Reduction of ammoniacal silver nitrate). Finally perform the two special tests for acetaldehyde given on p. 344 (Nitroprusside test and the Iodoform reaction). 

Acetaldehyde, CH3CHO, b.p. 21°, is generally used in aqueous solution, which has also a characteristic odour paraldehyde, (CH3CHO)3, is a liquid polymer, b.p. 124°, slightly soluble in water, odour similar to that of acetaldehyde, but less intense. Chloral, CCI3CHO, a liquid, is almost invariably encountered as the stable solid hydrate , CCl3CH(OH)2, m.p. 57 . Both have a characteristic odour the hydrate is readily soluble in water. 

As a general guide, however, it may be noted that the following have fairly easily recognisable odours methyl and ethyl formate methyl and ethyl acetate (apples) methyl and ethyl benzoate methyl salicylate (oil of winter-green) and ethyl salicylate methyl and ethyl cinnamate. (It is however usually impracticable to distinguish by odour alone between the methyl and ethyl esters of a particular acid.) Methyl and ethyl o. alate, and methyl and ethyl phthalate are almost odourless. Succinic and tartaric esters have faint odours. 

Salts of amines are generally soluble in water. Upon treatment with 10 per cent, sodium hydroxide solution, the amine will separate if it is insoluble or sparingly soluble in water if the amine is water-soluble, it can be partially volatilised by gentle warming and its presence will be suggested by a characteristic odour. 

Mercaptans RSH (also thioethers or sulphides R SR and disulphides R SSR") are generally hquids and possess unpleasant odours. 

Nitro compounds, when hquid, have characteristic odours, are insoluble in water, highly refractive and with a density greater than unity. Many are crystalline sohds. Most nitro compounds are slightly coloured, generally yellow the intensity of the colour increases with the number of nitro groups. The following reactions will assist in their detection. 

Moat phenols are crystalline solids notable exceptions are m-cresol and o-bromophenol. The monohydric phenols generally have characteristic odours. The solubihty in water increases with the number of hydroxl groups in the molecule. 

Aromatic nitriles are generally liquids or low melting point solids, and usually have characteristic odours. They give no ammonia with aqueous sodium hydroxide solution in the cold, are hydrolysed by boiling aqueous alkali but more slowly than primary amides ... 

Mercaptans and thiophenols (thiols). The thiols are generally liquids with penetrating and disagreeable odours, which persist even at extremely low concentrations in the air. They are soluble in dilute sodium hydroxide solution. Thiols are best characterised as the crystalline 2 4-dinitrophenyl thioethers or as the corresponding sulphones (see Section 111,168). 

The very low density materials (VLDPEs) introduced in the mid-1980s are generally considered as alternatives to plasticised PVC (Chapter 12) and ethylene-vinyl acetate (EVA) plastics (see Chapter 11). They have no volatile or extractable plasticisers as in plasticised PVC nor do they have the odour or moulding problems associated with EVA. Whilst VLDPE materials can match the flexibility of EVA they also have better environmental stress cracking resistance, improved toughness and a higher softening point. 

Property Units General purpose Medium shock High shock Electrical low loss Acid resistant Minimum odour Heat resistant BS 2782 test method... 

In a general comparison with phenolic resins, the U-F materials are cheaper, light in colour, are lacking in odour, have better resistance to electrical tracking but have an inferior heat resistance and a higher water absorption. 

Routine Vents General ventilation (factory atmosphere) Local extraction (dust, fumes, odour)... 

Commercial data sheets generally provide the following properties for the resins softening point colour degree of unsaturation acid number saponification number density ash content odour. 

Oils distilled in Kurope from imported Slngapoie leaves, which are of much finer odour than mosl of the native distilled oil, have in general the rollovving characters —... 

The fresh flowers of the mignonette, Heicda odoratu, yield traces, about -002 per oeut., of an essential oil of eieecdingiy powerful odour. This oil is semi-solid at ordinary temperatures, and its cberaistnr is not uoderslood, as the oil is in itself so very rare. Indeed, commercially, -an ordinary floral extract is generally used in preferenoe to any direct... 

Mehrling and Welde first determined if hydro-aromatic ring aldehydes in general gave violet like odours when condensed with acetone, and it was found that in the case of the four following aldehydes only the first yields a body having a violet odour —... 

It should also be noted that the lemon odour is not confined to the para isomers, as it is even more pronounced in several of the ortho and meta bodies, although generally modified. 

Unsaturated bodies, generally, have stronger odours than the corresponding saturated compounds and are known to possess more residual... 

Fatty Acid Esters of Methyl Alcohol.—The following esters of methyl alcohol are commercial products, and all have fruity odours, and are very suitable for blending with flower oils to impart distinctive secondary odours to them. They are, generally speaking, very expensive, some of them costing as much as 12 per lb., but, as only minute quantities... 

Styrolyl Acetate.—Styrolene alcohol, or phenyl-ethyl glycol, is an alcohol prepared from styrolene dibromide by the action of caustic potash. It can be esterified, and forms an acetic ester of the formula CgHj. CH(OH)CHg. OOC. CHg. It is an ester with a fine flower odour, which has been described as fragrant and dreamy . It is generally stated by those who have used it that it is indispensable in the preparation of fine flower bouquets with a jasmin odour. 

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