Cannizzaro reaction catalysts

Furfural can be oxidized to 2-furoic acid [88-14-2] reduced to 2-furanmethanol [98-00-0] referred to herein as furfuryl alcohol, or converted to furan by decarbonylation over selected catalysts. With concentrated sodium hydroxide, furfural undergoes the Cannizzaro reaction yielding both 2-furfuryl alcohol and sodium 2-furoate [57273-36-6]. 

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. 

Formaldehyde is readily reduced to methanol by hydrogen over many metal and metal oxide catalysts. It is oxidized to formic acid or carbon dioxide and water. The Cannizzaro reaction gives formic acid and methanol. Similarly, a vapor-phase Tischenko reaction is catalyzed by copper (34) and boric acid (38) to produce methyl formate ... 

Simple aliphatic nitriles, aldehydes, ketones and esters are not readily alkylated under liquiddiquid phase-transfer conditions. Direct alkylation of aldehydes under even mildly basic phase-transfer conditions has to compete with aldol and Cannizzaro reactions and yields are low and variable [e.g. 6], a,a-Disubstituted aldehydes are C-alkylated, e.g. formylcyclohexane has been alkylated (>70%) with a range of reagents using benzyltrimethylammonium isopropoxide as the basic catalyst [7], whereas a-unsubstituted alkanals tend to undergo aldol condensation under basic liquid liquid two-phase conditions [8]. 

Urea-formaldehyde resins are generally prepared by condensation in aqueous basic medium. Depending on the intended application, a 50-100% excess of formaldehyde is used. All bases are suitable as catalysts provided they are partially soluble in water. The most commonly used catalysts are the alkali hydroxides. The pH value of the alkaline solution should not exceed 8-9, on account of the possible Cannizzaro reaction of formaldehyde. Since the alkalinity of the solution drops in the course of the reaction, it is necessary either to use a buffer solution or to keep the pH constant by repeated additions of aqueous alkali hydroxide. Under these conditions the reaction time is about 10-20 min at 50-60 C. The course of the condensation can be monitored by titration of the unused formaldehyde with sodium hydrogen sulfite or hydroxylamine hydrochloride. These determinations must, however, be carried out quickly and at as low temperature as possible (10-15 °C), otherwise elimination of formaldehyde from the hydroxymethyl compounds already formed can falsify the analysis. The isolation of the soluble condensation products is not possible without special precautions, on account of the facile back-reaction it can be done by pumping off the water in vacuum below 60 °C imder weakly alkaline conditions, or better by careful freeze-drying. However, the further condensation to crosslinked products is nearly always performed with the original aqueous solution. 

Aldol condensations were originally carried out in the liquid phase and catalysed homogeneously by acids or bases this way of operation is still predominant. Solid-catalysed aldol reactions can also be performed in the liquid phase (in trickle or submerged beds of catalyst), but in many cases vapour phase systems are preferred the factors determining the choice are the boiling points and the stability of the reactants at elevated temperatures. At higher temperatures, the formation of a, j3-unsaturated aldehydes or ketones [reactions (B) and (C)] is preferred to aldol (ketol) formation [reaction (A)]. A side reaction, which may become important in some cases, is the self-condensation of the more reactive carbonyl compound if a mixed condensation of two different aldehydes or ketones is occurring. The Cannizzaro reaction of some aldehydes or polymerisation to polyols or other resin-like products can also accompany the main reaction. 

The lower reactivity of benzaldehyde with respect to acetaldehyde was found also in the vapour phase aldolisation over lithium phosphate [390]. Over the same catalyst, the reactivity order in the self-condensations of aldehydes could be estimated as CH3CHO > CH3CH2CHO (CH3)2-CHCHO. The reactivity of isobutyraldehyde in the self-condensation was almost undetectable, probably due to steric hindrance on the a-carbon, but this substance was able to react as a hydrogen acceptor with cyclohexanone. With propionaldehyde over a calcium hydroxide catalyst, a Cannizzaro-type reaction occurred to some extent simultaneously with the aldolisation [390]. This unexpected result was also recorded by other authors [391], who established that the tendency to aldolisation decreased, and the tendency to the Cannizzaro reaction increased, with... 

Condensation of dimethyl sulfone with benzaldehyde under PT conditions yeilds 3,5-diphenylthiadioxane S,S-dioxide (38). The product may be obtained in good yield, using TEBA or 18-crown-6.64 Gokel65 has shown that when the catalyst is a crown ether the reaction is complicated by the production of benzoic acid, presumably via a Cannizzaro reaction. 

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. 

In an attempt to couple halobenzaldehydes with amines, A1203 was pre-absorbed with the substituted benzaldehydes and imidazole or piperidine as a base and irradiated with microwaves. However, the corresponding benzylic alcohols and benzoic acids were unexpectedly obtained by the Cannizzaro route (Scheme 4.20). The products of Cannizzaro reactions were also obtained as the main products, when microwave-assisted condensation reactions of benzaldehydes with vinyl acetate using barium hydroxide as the catalyst were attempted40. 

Pourjavadi, A., Soleimanzadeh, B. and Malandi, G.B., Microwave-induced Cannizzaro reaction over neutral gamma-alumina as a polymeric catalyst, React. Funct. Polymers, 2002, 51, 49-53. 

Disproportionation (or dismutation) — Reaction in which species with the same oxidation state react with each other to yield one species of higher oxidation state and one of lower oxidation state, e.g., 3Au+ -> Au3+ + 2Au, or 4KCIO3 -> KC1 + 3KCIO4, or the d. reaction of an aldehyde in alkaline medium into the respective carboxylic acid and alcohol compounds, known as Cannizzaro reaction 2R - CHO + NaOH - R - COONa + R-CH2OH. In practice, d. happens rarely spontaneously, but is usually achieved by a catalyst application. 

Various methods, many with an eye towards industrial application, have been examined to accelerate Cannizzaro reactions. For example copper-silica catalysts,Na2S, Na2S203 or NaaSOs supported on AI2O3, and ultrasound all have been reported to accelerate certain Cannizzaro processes. An extremely promising development is the use of transition metal catalysts, which may be employed under neutral conditions in the absence of strong base. This permits the use of enolizable aldehydes like (28), which under basic conditions would immediately be consumed via aldol reactions. For example, in the presence... 

A mechanistically similar example is the Cannizzaro reaction, which is in essence a disproportionation between two aldehydes lacking a-hydrogen with a parallel addition of water to yield an alcohol and a carboxylic acid [144]. Aldol condensation cannot take place since the a-hydrogen is absent. Most likely the formation of aldehydrates takes place in the zeolite pores. NaX and NaY have been reported to be successful catalysts [150]. 

Silver, Ag, (as well as silver oxide, Ag20, and silver nitrate, AgN03), is used as a catalyst in the oxidation of aromatic aldehydes to carboxylic acids in the presence of alkalies (Cannizzaro reaction) [362, 363, 364]. 

When aldehyde, carrying an active a-hydrogen, is coupled with formaldehyde, the product becomes a suitable substrate for Cannizzaro reaction, which can react with formaldehyde subsequently in one pot to give the corresponding alcohol and sodium formate. Sodium hydroxide is believed to be a good catalyst for this reaction (O Scheme 8). 

New C-0 bonds are formed in the CO/H2 synthesis when CO is converted to CO2 by the WGS reaction (3) and in the synthesis of esters. Only the latter will be discussed here. Primarily methyl esters are formed, and they are significant side products over the (Cs)/Cu/ZnO catalysts but not over the alkali/(Co)/M0S2 catalysts. The mechanism for methyl ester formation has been suggested (ref. 39) to occur via a coupling of a Cn aldehyde with a Ci aldehyde by the Cannizzaro reaction or by a nucleophilic attack of a Cn aldehyde by methoxide (Tischenko reaction). The exception is the formation of methyl formate that occurs via a nucleophilic attack of CO by adsorbed methoxide e... 

These primarily concern the routes involving the use of formaldehyde in transformations of the Cannizzaro reaction type in the presence of catalysts based on padnk or alkaline, earth alkali metals etc. and passing through the following intermediates ... 

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