Aromatic alcohol

Aromatic alcohols (derivatives of carblnol HCHjOH) may be prepared (compare AltpAaltc Alcohols, discussion preceding Section 111,14)  

By the Cannizzaro reaction. This consists in the action of a concentrated aqueous solution of sodium or potassium hydroxide upon an aldehyde (see detailed discussion before Section IV, 123), for example  

Only half of the aldehyde is reduced to the alcohol, the other half being oxidised to the acid. By using a slight excess (say, 1 -3 mols) of aqueous formaldehyde, practically the whole of the aromatic aldehyde is converted into the alcohol the formaldehyde Is simultaneously oxidised to formic acid. This is sometimes termed a crossed Cannizzaro reaction. The example given is  

Benzaldehyde and veratraldehyde (Section IV, 194) may be similarly converted into the corresponding alcohols. 

Aromatic primary alcohols diflfer from aliphatic primary alcohols in that they react with concentrated hydrochloric acid in the cold to yield the corresponding chlorides, for example  

In aromatic alcohols, of which the simplest example is benzyl alcohol (phenylmethanol, 3), the hydroxyl group is present in an aliphatic side chain. Hence they are best regarded as aryl-substituted alcohols. Their properties are significantly different from those of phenols, but are typical of alcohols. 

Benzyl alcohol (3) can be synthesized by the hydrolysis of (chloromethyl)benzene (benzyl chloride) (see Chapter 9) and by the 

Reduction of the carbonyl function in acetophenones using sodium in ethanol also produces an alcohol. More complex aromatic alcohols may be prepared from carbonyl compounds by reaction with Grignard reagents followed by hydrolysis (see Chapter 10). 

Hydrogenolysi means the removal of a functional group and its replacement by hydrogen. 

ttie benzyl-o ygen bond is broken, a reaction that has proved important in peptide synthesis. Hydrogenation refers to the addition ot hydrogen to, for example, a C=C bond. 

The CH2OH group is ortholpara directing towards electrophilic attack. Nitration and sulfonation are possible, but care must be taken to avoid interaction with the hydroxyl group. It is sometimes preferable to carry out the electrophilic substitution reaction on the appropriate benzyl halide and then to hydrolyse the product to the substituted alcohol. 

Like saturated acyclic alcohols, aromatic alcohols, which are widely used in perfumery, 

It is a colorless liquid boils at 206°.5 (403°.7 F.) has an aromatic odor is insoluble in water, soluble in all proportions in alcohol, ether, and carbon disulfid. By oxidation it yields, first, benzoic aldehyde, C Hi(COH) and afterward, benzoic acid, CaHeiCOOH). By the same means it may be made to yield products similar to those obtained from the alcohols of the saturated hydrocarbons. 

These substances are intermediate in function between the-alcohols and the phenols, and contain both substituted groups (OH) and CH,OH. 

It is obtained from bitter almonds. The crude oil contains, besides benzoic aldehyde, hydrocyanic and benzoic acids and cyanobenzoyl. To purify it, it is treated with three to four times its volume of a concentrated solution of sodium bisulfite the crystalline mass is expressed, dissolved in a small quantity of water, and decomposed with a concentrated solution of sodium cai-bonate—the treatment being repeated, if necessary. 

When perfectly pure, benzoic aldehyde exerts no deleterious action when taken internally owing, however, to the diflBculty of completely removing the hydrocyanic acid, the substances usually sold as oil of hitter almonds, ratafia, and almond flavor, are almost always poisonous, if taken in sufficient quantity. They m.ay contain as much as 10-15 per cent, of hydrocyanic acid, although said to be purified. The jvesence of the poisonous substances may be detected by the tests given on page 292. 

Salicylic aldehyde—Salioyl hydrid—Salicylal—Salicylous acid —C H4(0H)C0H—122—exists in the flowers of Spirwa ulmaria, and is the principal ingredient of the essential oil of that plant. It is best obtained by oxidizing salicin q.v.). 

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Esterification with an aromatic alcohol may be readily achieved by using an excess of the acid. The latter is readily removed by washing with water and/or treatment with sodium bicarbonate solution, for example ... 

Aromatic alcohols are insoluble in water and usually burn with a smoky flame. Their boiling points are comparatively high some are solids at the ordinary temperature. Many may be oxidised by cautious addi-tion of dilute nitric acid to the corresponding aldehyde upon neutralis-tion of the excess of acid, the aldehyde may be isolated by ether extraction or steam distillation, and then identified as detailed under Aromatic Aldehydes, Section IV,135. 

Most aromatic alcohols exhibit the majority of the reactions given under Aliphatic Alcohols, Section 111,27, and may be converted into crystalline derivatives as there described. 

Table IV,205, contains the melting points of the derivatives of a number of commonly-occurring aromatic alcohols.

Benzyl alcohol (1) and P-phenethyl alcohol (2) (2-phenylethanol) are the simplest of the aromatic alcohols, and, as such, are chemically similar. Their physical properties are given in Table 1. 

For aromatic alcohols and compounds with an----OH on a side chain, the alcohol contribution (primary, etc.) must be included. For example, o-chlorophenol ... 

Solids. —It may Idc a hydrocM bon (c .g., paraffin wa, naphthalene) highei alcohol eg., cetyl alcohol) aldehyde e.g., z5-hydroxybenzaldehyde) ketone and qiiinonc e.g., benzo-phenone, camphor) acid (higher fatty, e.g., palmitic acid or aromatic acid) ester (of glycerol, phenols or aromatic alcohols) phenol e.g., thymol),... 

Benzyl alcohol, C Hj. CHjOH, is the lowest member of the normal series of aromatic alcohols containing the benzene nucleus. It exists to a certain extent in the free state, but more often in the form of esters, principally of acetic, benzoic, and cinnamic acids, in a number of essential oils, such as those of jasmin, tuberose, cassie fiowers, and ylang-ylang. 

An unusual by-product was obtained in small yield in palladium-catalyzed reduction of 2-amino-4,5-dimethoxyindanone hydrochloride, The reduction was done in two stages first, a rapid absorption of 1 mol of hydrogen at 38 C to give the amino alcohol, and then a much slower reduction in the presence of HCIO4 at 70 "C. The rearranged by-product was shown to arise from attack of acid on the amino alcohol (50), Resistance to hydrogenolysis is characteristic of / -amino aromatic alcohols (56), a fact that makes reduction of aromatic oximino ketones to amino benzyl alcohols a useful synthetic reaction. 

Chiralcel OB is associated with the separation of aromatic and nonaromatic sulfoxides and Chiralcel OD with aromatic alcohols. 

KU-2 and SG-50 Simple vinyl esters of aliphatic and aromatic alcohols 31... 

Generally the acid or protonated acid is observed. The aromatic alcohols can be differentiated by the loss of 18 Daltons from the molecular ion. 

Primary straight-chain and aromatic alcohols (also look for a large mJz 31 )... 

Aromatic compounds (C5H5) Aromatic nitro compounds Aromatic alcohols Vinyl furans... 

The present procedure was adapted from a general method of preparing aromatic alcohols recently described.5... 

In order to obtain anionic polyoxyethylene phosphate surfactants, either the terminal hydroxy group of a polyoxyethylated hydrophobic substance is reacted with a phosphorylating agent or a phosphate ester is oxalkylated. Most often aliphatic and aliphatic-aromatic alcohols are first treated with an alkylene oxide and afterward with one of the phosphorylating agents, such as P4OI0, POCl3, phosphoric acid, or polyphosphoric acid [39-48]. 

Interestingly, free nano-iron oxide particles are active catalysts for the selective oxidation of alcohols to yield the corresponding aldehydes/ketones [72, 73]. Different aromatic alcohols and secondary aliphatic alcohols were oxidized with high selectivity, but at low conversion. Here, further improvement should be possible (Scheme 25). 

In an effort directed at developing a racemization catalyst which works uniformly for all the substrates at room temperature, we designed and synthesized a novel aminocyclopentadienyl ruthenium chloride complex 5. The DKR of aromatic as well as aliphatic alcohols could be conducted at room temperature. In case of aromatic alcohols, the substituent effects were found insignificant in the DKR however, aromatic alcohols have comparatively faster conversion rates than their ahphatic counterparts. This is the first ever report of a catalyst... 

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