Aldehydes properties

It is marketed as a 35-40 per cent, solution in water (formalin). The rpactions of formaldehyde are partly typical of aldehydes and partly peculiar to itself. By evaporating an aqueous solution paraformaldehyde or paraform (CHjO), an amorphous white solid is produced it is insoluble in most solvents. When formaldehyde is distilled from a 60 per cent, solution containing 2 per cent, of sulphuric acid, it pol5unerises to a crystalline trimeride, trioxane, which can be extracted with methylene chloride this is crystalline (m.p. 62°, b.p. 115°), readily soluble in water, alcohol and ether, and devoid of aldehydic properties ... 

Vapour density determinations show that paraldehyde is formed by the union of three molecules of acetaldehyde. Since the substance has no aldehydic properties the following structure, that of a cyclic triacetal, is properly given to it ... 

Like paraldehyde, metaldehyde can be preserved, and, when freshly prepared, is odourless. It also has no aldehydic properties. On keeping, however, a distinct odour of acetaldehyde becomes evident —a sign that here also an equilibrium is slowly being established. Metaldehyde can be completely depolymerised by heating. Molecular weight determinations (in phenol) show that metaldehyde is tetra-molecular (Hantzsch) the examination of the space lattice of crystals by the method of Laue and Bragg points to the same conclusion (Mark). 

The loss of aldehyde properties by a change in the aldehyde group is due to the union of the three molecules into a ring. The isomerism of the two polymers is probably due to different space relations, i.e., it is stereo-isomerism. The following formula has been suggested. 

Reduction of a-thebaizone with hydrogen and platinum oxide in methanol affords phenolic dihydrothebaizone [xxiv], whereas reduction with aluminium amalgam in wet ether yields desoxythebaizone, also obtained by reduction with zinc and hydrochloric acid. Desoxythebaizone shows no aldehydic properties and has been allotted the structure [xxv] it gives dihydrodesoxythebaizone on hydrogenation and dihydrodesoxythebaizonic acid on hydrolysis and hydrogenation [112]. Those two substances may be allotted the formulae [xxvi, R = Me] and [xxvr, R = H] respectively, though as desoxythebaizone is an allylio other they may bo phenols and havo the structures [xxvn, R Mo] and [xxvn, R J-l. ... 

Which of the above compounds show both acid and aldehyde properties ... 

Definition Volatile oil from fresh leaves and twigs of Meiaieuca ieucadendron, contg. 50-60% eucalyptol and l-pinene, terpineol, and aldehydes Properties Colorless of yish. liq., agreeable camphor odor, bitter aromatic taste misc. with alcohol, chloroform, ether, CS2 very si. sol. in water sol. in 1 vol. 80% alcohol dens. 0.912-0.925 ref. index 1.4660-1.4710 (20 C)... 

Plates from EtOH. M.p. 50° (45-6°). Sol. EtOH, EtjO. Very spar. sm. hot 1 0. Volatile in steam. Very feeble aldehydic properties. 

Phenylhydrazine on exposure to light slowly darkens and eventually becomes deep red in colour salts of the base share this property but to a lesser degree, the sulphate and acetate (of the common salts) being most stable to light. Phenylhydrazine is largely used in organic chemistry to characterise aldehydes and ketones as their phenyl-hydrazones (pp. 342, 345), and carbohydrates as their osazones (pp. 136-140). It is readily reduced thus in the process of osazone formation some of the phenylhydrazine is reduced to aniline and ammonia. On the... 

In a 500 ml. flask, fitted with a reflux condenser, place 53 g. of 1-chloro-methylnaphthalene (Section IV.23), 84 g, of hexamethylenetetramine and 250 ml. of 1 1 acetic acid [CAUTION 1-Chloromethylnaphtha-lene and, to a lesser degree, a-naphthaldehyde have lachrymatory and vesicant properties adequate precautions should therefore be taken to avoid contact with these substances.] Heat the mixture under reflux for 2 hours it becomes homogeneous after about 15 minutes and then an oil commences to separate. Add 100 ml. of concentrated hydrochloric acid and reflux for a further 15 minutes this will hydrolyse any SchifiF s bases which may be formed from amine and aldehyde present and will also convert any amines into the ether-insoluble hydrochlorides. Cool, and extract the mixture with 150 ml. of ether. Wash the ether layer with three 50 ml. portions of water, then cautiously with 50 ml. of 10 per cent, sodium carbonate solution, followed by 50 ml. of water. Dry the ethereal solution with anhydrous magnesium sulphate, remove the ether by distillation on a steam bath, and distil the residue under reduced pressure. Collect the a-naphthaldehyde at 160-162718 mm. the yield is 38 g. 

If an unknown compound gives a positive test with the 2 4-dinitrophenylhydrazine reagent, it then becomes necessary to decide whether it is an aldehyde or a ketone. Although the dimedone reagent (Section 111,70,2) reacts only with aldehydes, it is hardly satisfactory for routine use in class reactions. It is much simpler to make use of three other reagents given below, the preparation and properties of which have already been described (Section 111,70). 

The production of both an alcohol and the sodium salt of an acid might easily be confused with the hydrolysis products of an ester (in the above instance benzyl benzoate). Such an error would soon be discovered (e.g., by reference to the b.p. and other physical properties), but it would lead to an unnecessary expenditure of time and energy. The above example, however, emphasises the importance of conducting the class reactions of neutral oxygen-containing compounds in the proper order, viz., (1) aldehydes and ketones, (2) esters and anhydrides, (3) alcohols, and (4) ethers. 

Separations based upon differences in the chemical properties of the components. Thus a mixture of toluene and anihne may be separated by extraction with dilute hydrochloric acid the aniline passes into the aqueous layer in the form of the salt, anihne hydrochloride, and may be recovered by neutralisation. Similarly, a mixture of phenol and toluene may be separated by treatment with dilute sodium hydroxide. The above examples are, of comse, simple apphcations of the fact that the various components fah into different solubihty groups (compare Section XI,5). Another example is the separation of a mixture of di-n-butyl ether and chlorobenzene concentrated sulphuric acid dissolves only the w-butyl other and it may be recovered from solution by dilution with water. With some classes of compounds, e.g., unsaturated compounds, concentrated sulphuric acid leads to polymerisation, sulphona-tion, etc., so that the original component cannot be recovered unchanged this solvent, therefore, possesses hmited apphcation. Phenols may be separated from acids (for example, o-cresol from benzoic acid) by a dilute solution of sodium bicarbonate the weakly acidic phenols (and also enols) are not converted into salts by this reagent and may be removed by ether extraction or by other means the acids pass into solution as the sodium salts and may be recovered after acidification. Aldehydes, e.g., benzaldehyde, may be separated from liquid hydrocarbons and other neutral, water-insoluble hquid compounds by shaking with a solution of sodium bisulphite the aldehyde forms a sohd bisulphite compound, which may be filtered off and decomposed with dilute acid or with sodium bicarbonate solution in order to recover the aldehyde. 

In 1884, Nencki (70), studying the properties of rhodaninic acid, confirmed the formula proposed by Libermann and Lange (39) and noted its ability to condense with aldehydes. 

By analogy to the hydration of alkenes hydration of an alkyne is expected to yield an alcohol The kind of alcohol however would be of a special kind one m which the hydroxyl group is a substituent on a carbon-carbon double bond This type of alcohol IS called an enol (the double bond suffix ene plus the alcohol suffix ol) An important property of enols is their rapid isomerization to aldehydes or ketones under the condi tions of their formation... 

In the preceding chapter you learned that nucleophilic addition to the carbonyl group IS one of the fundamental reaction types of organic chemistry In addition to its own reactivity a carbonyl group can affect the chemical properties of aldehydes and ketones m other ways Aldehydes and ketones having at least one hydrogen on a carbon next to the carbonyl are m equilibrium with their enol isomers... 

Aldol condensation offers an effective route to a p unsaturated aldehydes and ketones These compounds have some interesting properties that result from conjugation of the carbon-carbon double bond with the carbonyl group As shown m Figure 18 6 the rr systems of the carbon-carbon and carbon-oxygen double bonds overlap to form an extended rr system that permits increased electron delocalization... 

You have already had considerable experience with carbanionic compounds and their applications in synthetic organic chemistry The first was acetyhde ion m Chapter 9 followed m Chapter 14 by organometallic compounds—Grignard reagents for example—that act as sources of negatively polarized carbon In Chapter 18 you learned that enolate ions—reactive intermediates generated from aldehydes and ketones—are nucleophilic and that this property can be used to advantage as a method for carbon-carbon bond formation... 

A characteristic property of an aldehyde function is its sensitivity to oxidation A solu tion of copper(II) sulfate as its citrate complex (Benedict s reagent) is capable of oxi dizing aliphatic aldehydes to the corresponding carboxylic acid... 

TABLE D Selected Physical Properties of Representative Aldehydes and Ketones... 

Furfural—acetone resins have been used to form resin-aggregate mixtures referred to as organic concretes. Despite the reportedly excellent properties, there has been virtually no commercial use of such resins outside the former Soviet Union. The stmctures and polymerization mechanisms of these furfural—aldehyde—ketone polymers are discussed in a review (6). 

Formaldehyde polymers have been known for some time (1) and early investigations of formaldehyde polymerization contributed significantly to the development of several basic concepts of polymer science (2). Polymers of higher aUphatic homologues of formaldehyde are also well known (3) and frequently referred to as aldehyde polymers (4). Some have curious properties, but none are commercially important. 

Chemical Properties. A combination of excellent chemical and mechanical properties at elevated temperatures result in high performance service in the chemical processing industry. Teflon PEA resins have been exposed to a variety of organic and inorganic compounds commonly encountered in chemical service (26). They are not attacked by inorganic acids, bases, halogens, metal salt solutions, organic acids, and anhydrides. Aromatic and ahphatic hydrocarbons, alcohols, aldehydes, ketones, ethers, amines, esters, chlorinated compounds, and other polymer solvents have Httle effect. However, like other perfluorinated polymers,they react with alkah metals and elemental fluorine. 

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