Alcohol with aldehydes and ketones

Treatment of poly(vinyl alcohol) with aldehydes and ketones leads to the formation of poly(vinyl acetals) and poly(vinyl ketals), of which only the former products are of any commercial significance Figure 14.7). 

The reactions of alcohols with aldehydes and ketones are related to the reactions of alcohols with acids (esterification) discussed in the preceding section. Both types involve addition of alcohols to carbonyl groups, and both are acid-catalyzed. 

Alcohols with Aldehydes and Ketones,—When an essential oil contains, besides the alcoholic compounds, also aldehydes and ketones, the determination of the alcohols by acetylation is no longer accurate, since aldehydes and ketones react with acetic anhydride. In such cases the aldehydes may be eliminated by means of their insoluble compounds with alkaline bisulphite or other reagent see paragraph 10 Detection of... 

Hemiacetals from reaction of alcohols with aldehydes and ketones... 

Dioxolanes 162 are formed by the reaction of diacetylenic alcohols with aldehydes and ketones in the presence of base -. The initial step involves formation of the... 

HEMIACETALS FROM REACTION OF ALCOHOLS WITH ALDEHYDES AND KETONES... 

In our discussion of carbohydrate sttucture to this point, we have already encountered an important reaction—the formation of glycosides under acid-catalyzed conditions (see Section 23.14). Glycoside formation draws our attention to the fact that an OH group on the anomeric carbcMi of a pyranose or furanose differs in reactivity from the other hydroxyl groups of the carbohydrate. It also demonstrates that what looks like a new reaction is one that we ve encountered before— in this case, acetal formation that occurs in the reactions of alcohols with aldehydes and ketones (see Section 17.8). Many other reactions of carbohydrates are also related to familiar functional-group transformations some of these are recounted in Table 23.2. 

A. Condensation of Alcohols with Aldehydes and Ketones 34-1. Preparation of Acetal (I,t-Diethoxyethane)... 

Organohthium and organomagnesium compounds find their chief use m the prepa ration of alcohols by reaction with aldehydes and ketones Before discussing these reac tions let us first examine the reactions of these organometallic compounds with proton donors... 

Synthesis of alcohols using organolithi um reagents (Section 14 7) Organolithi um reagents react with aldehydes and ketones in a manner similar to that of Grignard reagents to produce alcohols... 

Sodium acetylide and acetylenic Grignard reagents react with aldehydes and ketones to give alcohols of the type... 

The mechanisms by which transition metal oxidizing agents convert alcohols to aldehydes and ketones are complicated with respect to their inorganic chemistry The organic chemistry is clearer and one possible mechanism is outlined m Figure 15 4 The... 

Many esters occur naturally Those of low molecular weight are fairly volatile and many have pleasing odors Esters often form a significant fraction of the fragrant oil of fruits and flowers The aroma of oranges for example contains 30 different esters along with 10 carboxylic acids 34 alcohols 34 aldehydes and ketones and 36 hydrocarbons... 

Organolithium and organomagnesium reagents are highly reactive toward most carbonyl compounds. With aldehydes and ketones, the tetrahedral adduct is stable, and alcohols are isolated after protonation of the adduct, which is an alkoxide ion. 

If homolytic reaction conditions (heat and nonpolar solvents) can be avoided and if the reaction is conducted in the presence of a weak base, lead tetraacetate is an efficient oxidant for the conversion of primary and secondary alcohols to aldehydes and ketones. The yield of product is in many cases better than that obtained by oxidation with chromium trioxide. The reaction in pyridine is moderately slow the intial red pyridine complex turns to a yellow solution as the reaction progresses, the color change thus serving as an indicator. The method is surprisingly mild and free of side reactions. Thus 17a-ethinyl-17jS-hydroxy steroids are not attacked and 5a-hydroxy-3-ket-ones are not dehydrated. 

All that has been said in this section applies with equal force to the use of organo-lithium reagents in the synthesis of alcohols. Grignard reagents are one source of nucleophilic carbon organolithium reagents are another. Both have substantial carbanionic char acter in their- car bon-metal bonds and undergo the same kind of reaction with aldehydes and ketones. 

Complexes [Ru30(0Ac)6L3]"+ (L = H20, PPh3) have been found to be catalysts for the oxidation of primary and secondary alcohols to aldehydes and ketones under fairly mild conditions (65°C, 3 atm 02) with high catalytic turnovers [104],... 

For lists of reagents (with references) that condense with aldehydes and ketones to give alkene products, see Ref. 58, pp. 167,180. For those that give the alcohol product, see Ref. 58, pp. 575, 868, 875, 878, 901, 910. 

---