Crossed-Cannizzaro reaction

The analogous dismutation of furfural is described in Section V,8. For crossed Cannizzaro reaction , see discussion following Section IV,199. 

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 ... 

The base-catalyzed reaction of acetaldehyde with excess formaldehyde [50-00-0] is the commercial route to pentaerythritol [115-77-5]. The aldol condensation of three moles of formaldehyde with one mole of acetaldehyde is foUowed by a crossed Cannizzaro reaction between pentaerythrose, the intermediate product, and formaldehyde to give pentaerythritol (57). The process proceeds to completion without isolation of the intermediate. Pentaerythrose [3818-32-4] has also been made by condensing acetaldehyde and formaldehyde at 45°C using magnesium oxide as a catalyst (58). The vapor-phase reaction of acetaldehyde and formaldehyde at 475°C over a catalyst composed of lanthanum oxide on siHca gel gives acrolein [107-02-8] (59). 

Pentaerythritol is produced by reaction of formaldehyde [50-00-0] and acetaldehyde [75-07-0] in the presence of a basic catalyst, generally an alkah or alkaline-earth hydroxide. Reaction proceeds by aldol addition to the carbon adjacent to the hydroxyl on the acetaldehyde. The pentaerythrose [3818-32-4] so produced is converted to pentaerythritol by a crossed Cannizzaro reaction using formaldehyde. All reaction steps are reversible except the last, which allows completion of the reaction and high yield industrial production. 

The synthetic importance of the reaction is limited, because as a consequence of the disproportionation, the yield of the alcohol as well as the carboxylic acid is restricted to 50%. However good yields of alcohols can often be obtained when the reaction is carried out in the presence of equimolar amounts of formaldehyde. The formaldehyde is oxidized to formic acid and concomitantly reduces the other aldehyde to the desired alcohol. This variant is called the crossed Cannizzaro reaction. 

The reaction can be stopped at this point, but more often a second mole of formaldehyde is permitted to reduce the newly formed aldol to a 1,3-diol, in a crossed Cannizzaro reaction (19-60). If the aldehyde or ketone has several a-hydrogens, they can all be replaced. An important use of the reaction is to prepare pentaerythritol from acetaldehyde ... 

For a microwave assisted crossed Cannizzaro reaction, see Varma, R.S. Naicker, K.P. Liesen, P.J. Tetrahedron Lett 1998, 39, 8437. 

Scheme 6.40 Solvent-free crossed Cannizzaro reaction using paraformaldehyde.

Canned motor pumps, 27 76-78 Canned pet foods, 70 849 Cannel coal, 6 705 Cannizzaro reaction, 72 110 solid-state crossed, 76 574 Cannon-Fenske viscometer, 27 728 Canoe fragrances, 75 360 Canonical ensemble, 7 33 Cans, two- and three-piece, 75 37-38. 

Chemical reduction of aromatic aldehydes to alcohols was accomplished with lithium aluminum hydride [5i], alane [770], lithium borohydride [750], sodium borohydride [757], sodium trimethoxyborohydride [99], tetrabutylam-monium borohydride [777], tetrabutylammonium cyanoborohydride [757], B-3-pinanyl-9-borabicyclo[3.3.1]nonane [709], tributylstannane [756], diphenylstan-nane [114], sodium dithionite [262], isopropyl alcohol [755], formaldehyde (crossed Cannizzaro reaction) [i7i] and others. 

A crossed Cannizzaro reaction is similar to a normal Cannizzaro reaction however, two different aldehydes are reacting. Normally one of the aldehydes is formaldehyde because there are fewer chances for side reactions. (It also has the advantage of being cheap.) The reactions in Figures 11-34 and 11-35 are crossed Cannizzaro reactions using an excess of formaldehyde. The excess of formaldehyde increases the probability of the initial attack by the hydroxide being on the formaldehyde instead of the other aldehyde. Figure 11-35 shows the synthesis of pentaerythritol. 

A crossed Cannizzaro reaction with excess formaldehyde. 

Crossed Cannizzaro Reaction A Cannizzaro reaction involving two different aldehydes. 

Polyacetal resins have a repeating unit of -O-CH2-. They are strong, stiff polymers for valves, hoses, and tube connectors. Pentaerythritol finds end-uses in alkyd resins and explosives (pentaerythritol tetranitrate). To appreciate this synthesis, the student should review two condensation reactions, the crossed aldol and the crossed Cannizzaro. Acetaldehyde reacts with 3 mol of formaldehyde in three successive aldol condensations. This product then undergoes a Cannizzaro reaction with formaldehyde. 

Pentaerythritol, used in the production of alkyds, is produced by a crossed Cannizzaro reaction of the aldol condensation product of formaldehyde and acetaldehyde. The by-product formate salt is a major source of formic acid. 

Problem 15.21 For the Cannizzaro reaction, indicate (a) why the reaction cannot be used with aldehydes having an a H, —CHCHO (b) the role of OH and OD (Problem 15.20) (c) the reaction product with ethanedial, 0==CH—CH==0 (d) the reaction products of a crossed-Cannizzaro reaction between (i) formaldehyde and benzaldehyde, (ii) benzaldehyde and p-chlorobenzaldehyde. ... 

This is an internal crossed-Cannizzaro reaction the keto group is reduced and the —CHO is oxidized. 

The first reaction provides a route for the reduction of alkyl halides since the carbo-cation (isopropyl, in Rl) may be prepared from action of AICI3 on the corresponding alkyl halide. Reactions of the type Rl are also important in the process, catalytic cracking, in the manufacture of gasoline. They have also been studied in mass spectro-metric experiments [235]. Reaction R2 is one route to the preparation of carbocations under stable ion conditions. Reaction R3 is employed in the laboratory synthesis of the tropylium cation. Reaction R4, the (crossed) Cannizzaro reaction, is unusual in that it takes place under strongly basic conditions. The oxy dianion is an intermediate in the reaction of concentrated hydroxide with the aldehyde, R HO. None of R1, R2, or R3 may have hydrogen atoms a to the carbonyl groups. Formaldehyde (R1 = H) is readily... 

The aldol addition of formaldehyde in the presence of sodium hydroxide for the introduction of a hydroxymethyl branch was first applied to l,2 3,4-di-0-isopropylidene-aWefiydo-L-arabinose, and the product (143), formed by a crossed-Cannizzaro reaction, was converted into 1 by... 

Manufacture. Commercial preparation of neopentyl glycol can be via an alkali-catalyzed condensation of isobutyraldehyde with 2 moles of formaldehyde (crossed Cannizzaro reaction) (2,8). Yields are 70%. 

Cyclocitral (540) behaves as a nucleophile towards benzaldehyde and in the presence of sodium hydroxide the fused pyran-2-oI (541) is formed through an aldol (Scheme 202) (81JHC549). However, when sodium ethoxide is used as the catalyst, the pyran-2-one is produced. It is proposed that oxidation arises through a crossed Cannizzaro reaction with benzaldehyde (and much benzyl alcohol is observed in support of this idea), followed by a carbanion attack on more benzaldehyde and subsequent cyclization. 

CANNIZZARO REACTION. Base catalyzed dismulation of aromatic aldehydes or aliphatic aldehydes with no a-hydrogen into the corresponding acids and alcohols. When the aldehydes arc not identical, the reaction is called the "crossed Cannizzaro reaction."... 

A commercially important mixed addition involves ethanal and an excess of methanal in the presence of calcium hydroxide. Addition occurs three times and the resulting trihydroxymethylethanal (which has no a hydrogens) undergoes a crossed Cannizzaro reaction (see Exercise 16-33) with more methanal to give a tetrahydroxy alcohol known as pentaerythritol ... 

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