Tollens reaction formaldehyde

In Tollens reaction an aldehyde or ketone containing an a hydrogen is treated with formaldehyde in the presence of Ca(OH)2 or a similar base. The first step is a mixed aldol reaction (6-39). 

In the Cannizzaro reaction, the hydride ion that is being used to effect this reduction may come from an aldehyde that lacks an a-hydrogen atom, e.g. methanal or benzaldehyde. The receiving molecule may be a second molecule of the same aldehyde or a different one. The reaction requires a strong base, and the rate law is found to depend on the square of the concentration of the aldehyde and either the concentration or the square of the concentration of the base used. Overall a carboxylate anion and an alcohol are formed from two molecules of the aldehyde(s). The reaction may occur intramolecularly, i.e. a-ketoaldehydes give the a-hydroxycarboxylic acids on treatment with hydroxide ions. A variation of this process is called the Tollens reaction. In this case, a ketone or aldehyde that contains an a-hydrogen is treated with formaldehyde in the presence of Ca(OH)2. 

Tollens reaction The reaction of an aldehyde or ketone that has an a-hydrogen with formaldehyde, in the presence of Ca(OH)2 to give initially a mixed aldol product this is then usually reduced by... 

Historical. PE was first isolated by Tollens who was examining the effect of heat and reagents on formaldehyde. Apparently the crude formaldehyde he was working with contained a small % of acetaldehyde, which accounts for the PE formed. Although Tollens isolated it in 1882, it was not identified as PE until 1888 (Ref 2). Further details of the prepn and props of PE appeared in 1891 (Ref 3). The prepn is essentially a condensation betw 3 moles of formaldehyde and 1 of acetaldehyde to give an intermediate tris(hydroxymethyl)-acetaldehyde which is not isolated. An Intermolecular oxidn/redn then takes place betw this intermediate, and a 4th mole of formaldehyde, giving PE and formic ac (Ref 13, p 2). This type reaction is discussed under Cannizzaro Reaction in the Encycl (Vol 2, C25)... 

Pentaerythritol was obtained by Tollens and Wigand in 1891 [2] from acetaldehyde and formaldehyde according to the following reaction ... 

Barth, Snow and Wood [4] have proposed another reaction scheme approaching to that outlined by Tollens and Wigand [2], in which they assume that formaldehyde is present in the form of a polyoxymethylene chain ... 

It was first obtained by Hertz [67] who proposed its use as an explosive, since (in the authors opinion) it develops greater explosive strength that PETN but is less sensitive. Tollens and Apel [68] have prepared the initial alcohol (m.p. 156°C) resulting from the reaction of acetone with formaldehyde in the presence of calcium hydroxide, to which they attributed the structure of an enneaheptitol anhydride without, however, determining which hydroxyl groups were dehydrated. 

The Tollens condensation is a crossed aldolization employing formaldehyde and an aldehyde or a ketone in the presence of a weak base. Since formaldehyde has no -hydrogen atoms, it is an extremely reactive carbanion acceptor (p. 155). Consequently, reaction occurs readily with carbanions and leads to polymethylol derivatives 6... 

Amino resin chemistry goes back to the 1880s. The first mention of a urea-formaldehyde reaction product was by Tollens (9) in 1884 in a report of work done by an associate named Holzer. Very few references relating to amino resins can be found in the chemical literature prior to 1900. Ludy (10) in 1889 and Carl Goldschmidt (11) in 1896 mentioned products that were similar to the material... 

The first aminoplast based on urea-formaldehyde (UF) was obtained and patented in 1918 by John through the polycondensation of urea with formaldehyde, although this reaction was first described in 1884 by Tollens [4]. Unlike the phenolics, the UF could be moulded into light-coloured articles and they rapidly achieved commercial success. Paper impregnated with UF resin was used as an outer surface layer of decorative laminate in 1931, and the polycondensation of melamine with formaldehyde led to a new aminoplast resin in 1933 [5]. 

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