Odour, chemical

Polysubstituted 3-thiofiirans which are receiving a great interest as flavour and odour chemicals have been obtained by mono-//J5osubstitution and ortho-metallation from 3,4-dibromofuran <96T4065>. Dihydrofuran is used in a new synthesis of ketones from acids via acyl hemiacetals (Scheme 8, <96JOC6071>). 

Odour Chemical Sensing Temperature Spike-Train... 

BrCHi CHjBr. A colourless liquid with a sweet odour, m.p. 10°C, b.p. 132°C. Manufactured by passing ethene through bromine or bromine and water at about 20 C. Chemical properties similar to those of 1,2-dichloroethane when heated with alkali hydroxides, vinyl bromide is formed. Used extensively in petrols to combine with the lead formed by the decomposition of lead tetraethyl, as a fumigant for stored products and as a nematocide. 

CH2C1 CH2C1. Colourless liquid with an odour like that of chloroform b.p. 84 C. It is an excellent solvent for fats and waxes. Was first known as oil of Dutch chemists . Manufactured by the vapour- or liquid-phase reaction of ethene and chlorine in the presence of a catalyst. It reacts with anhydrous ethano-ales to give ethylene glycol diethanoate and with ammonia to give elhylenediamine, these reactions being employed for the manufacture of these chemicals. It burns only with difficulty and is not decomposed by boiling water. 

Dimeihylamine, C2H7N, (CH3)2NH. Colourless, inflammable liquid with an ammoniacal odour, mp -96" C, b.p. 7°C. Occurs naturally in herring brine. Prepared in the laboratory by treating nitrosodimetbyl-aniline with a hot solution of sodium hydroxide. Dimethylamine is largely used in the manufacture of other chemicals. These include the solvents dimethylacetamide and dimethyl-formamide, the rocket propellant unsym-metrical dimethylhydrazine, surface-active agents, herbicides, fungicides and rubber accelerators. 

CH rCHCH NHCSNH. Colourless crystalline solid with a faint garlic-like odour m.p. 74 C. Manufactured by treating propenyl isothiocyanate with a solution of ammonia in alcohol. It has been given by injection in the treatment of conditions associated with the formation of excessive fibrous tissue. Toxic side reactions may occur. Propenyl thiourea is a chemical sensitizer for photographic silver halide emulsions. 

Diethyl ether is a mobile, colourless liquid having b.p. 35° and dy 0720. It has a characteristic odour, and a burning taste. It is used chiefly as a solvent, and was formerly widely used as an anaesthetic owing to its chemical non-reactivity, it is very seldom used actually as a reagent, except in the preparation of Grignard reagents (p. 280) where probably its chemical properties reinforce its solvent action. 

Ethyl acetoacetate is a colourless liquid, d, i 03, slightly soluble in water, but almost insoluble in brine. It has a faint but pleasant odour. It is widely used in chemical syntheses. 

Physical Properties. Benzene, C H, toluene, C Hj-CH, and petrol (a mixture of aliphatic hydrocarbons, e.g., pentane, hexane, etc.) are colourless liquids, insoluble in and lighter than water. Benzene and toluene, which have similar odours, are not readily distinguishable chemically, and their physical constants should therefore be carefully noted benzene, m.p. 5 (solidifies when a few ml. in a dry test-tube are chilled in ice-water), b.p. 8i toluene, m.p. —93°, b.p. 110°. Petroleum has a characteristic odour. 

Hazard recognition and assessment always start from a knowledge of the individual properties of a chemical. What this may include is exemplified by Table 1.3. Additional properties, including those in Table 1.4, are relevant to environmental hazards, e.g. relating to behaviour on spillage or emission, and determination of permissible levels for disposal to air, land or water systems. Other properties may be relevant, e.g. odour which can serve as an, albeit often unreliable, means of detection. (Refer to Table 5.12.)... 

Characteristics evaluate as appropriate under all process conditions Formula (chemical structure) Purity (identity of any contaminants), physical state, appearance, other relevant information Concentration, odour, detectable concentration, taste ... 

The odour of a toxic chemical may be masked by the odour from another substance, or a mixture. 

Hydrogen sulphide Various chemical processes Odours, toxic... 

Thiazyl trifluoride, a colourless gas with a pungent odour, is prepared by the oxidative decomposition of FC(0)NSF2 with Agp2 (Eq. 8.5).NSF3 is kinetically very stable even in the liquid form. The chemical inertness of NSF3 resembles that of SFe. For example, it does not react with sodium metal below 200°C. ... 

L niney- has examined an apnarenily autbunlic sample of this oil, which liad an exceedingly One odour, and w hich had characters falling outside the above-ruentiooed limits. Its physical and chemical characters were as follows —... 

The connections between chemical constitution, on the one hand, and colour or physiological action on the other have been continually studied for many years, but the allied property of odour has only engaged occasional attention within quite recent times. 

Teudt considers that the nasal sensory nerves have electron vibrations which are increased by resonance when odoriferous substances having corresponding intramolecular electron vibrations are inspired with air, and he concludes that a chemical element can the more readily induce odour in... 

The well-known phenomenon of smell-fatigue is explained by the theory that actual chemical reaction takes place between the odoriferous body and some reacting material in the nose thus it can easily be conceived that some sort of addition reaction takes place and that directly the osmoceptor in the nose becomes saturated no further reaction is possible and no further odour can be appreciated until fresh osmoceptor has been formed. Ruzicka has suggested that two such osmoceptors are involved since substances inspired in a concentrated state have odours different to those perceived in a dilute condition. He suggests that one osmoceptor reacts more readily than the other and in consequence is the more readily saturated or consumed, this osmoceptor is responsible for the sensation produced when dilute odours are inspired. If the odour be concentrated, the first osmoceptor is saturated almost instantaneously and then the sensation produced is the result of the reaction between the odoriferous substance and the second osmoceptor. 

It will be realised that the strength of an odour may suffer successive diminutions in the process of smelling. It will be governed firstly, by the vapour pressure. of the odoriferous body, secondly, by the degree of solubility of the substance in water, thirdly, to its relative solubility in the lipoid fats with respect to that in water, and, lastly, to the speed of the chemical reaction. To a less extent the type of odour is similarly governed and this may account for the many shades of odour that exist. It is obvious that too much importance must not be placed on the chemical aspect of the problem, especially as regards the strength of an odour. 

The first publication of importance regarding the relationship between odour and chemical constitution per se, is that of Klimont, who attempted an explanation on the lines of Witt s colour theory. Elimont introduced the term aromataphore to designate groups which carry a pleasant odour with them. ... 

The lack of connection between the two phenomena is, of course, to be expected since colour is an objective phenomenon whereas odour is subjective, or, as Euzicka puts it, colour has a physical and odour a chemical influence on the human senses. 

Durrans in 1919 attempted to develop a theory based on the examination of the odours of substances considered class by class, and expressed the opinion that, from a chemical point of view, odour is caused primarily by the presence of unsatisfied or residual afiinity, but that the possession or otherwise of an odour by a body depends on physiological and physical as well as chemical properties. This theory, which is named the Residual Affinity Theory of Odour, demands that if a substance has an odour, it must answer to the following requirements — ... 

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