Formaldehyde, reaction with hydroxide

Even this is not all. A fourth molecule of formaldehyde reacts with hydroxide ion and then reduces the third aldol. This reduction is known as the Cannizzaro reaction, and is described in the box. The final product is the highly symmetrical pentaerythritol , CfCTbOH) with four CH2OH groups joined in a tetrahedral array about the same carbon atom. 

The last decade has seen quite remarkable advances in our knowledge of the structure and properties of the proanthocyanidins. Viscosity measurements were made of solutions of procyanidins isolated from Theobroma cacao and Chaenomeles speciosa with number-average degrees of polymerization of 6.1 and 11.8, respectively, in water and 1% sodium hydroxide at 25 °C. Procyanidins are apparently completely crosslinked by formaldehyde up to a chain length of 6 units, but few units are crosslinked in polymeric procyanidins. The second order rate constants observed for the formaldehyde reaction with catechin or epicatechin are approximately six times higher than that observed for the C. speciosa polymer. 

Ab initio molecular orbital calculations are being used to study the reactions of anionic nucleophiles with carbonyl compounds in the gas phase. A rich variety of energy surfaces is found as shown here for reactions of hydroxide ion with methyl formate and formaldehyde, chloride ion with formyl and acetyl chloride, and fluoride ion with formyl fluoride. Extension of these investigations to determine the influence of solvation on the energy profiles is also underway the statistical mechanics approach is outlined and illustrated by results from Monte Carlo simulations for the addition of hydroxide ion to formaldehyde in water. 

The material is produced from naphthalene by oleum or sulfur trioxide sulfonation under conditions conducive to the formation of the h sulfonate. Subsequent reaction with formaldehyde leads to polymerization and the sulfonic acid is neutralized with sodium hydroxide [17] or lime. The process is illustrated in Fig. 2.2. The value of n is typically low but conditions are chosen to get a proportion of higher-molecular-weight product as it is believed to be more effective [18]. The quantity of sodium sulfate by-product formed by the neutralization of excess sulfonating reagent will vary depending on the process used, but can be reduced by a subsequent precipitation process using lime [19]. 

It is reported that an industrial explosion was initiated by charging potassium hydroxide in place of potassium carbonate to the chloro-nitro compound in the sulfoxide [1], Dry potassium carbonate is a useful base for nucleophilic displacement of chlorine in such systems, reaction being controlled by addition of the nucleophile. The carbonate is not soluble in DMSO and possesses no significant nucleophilic activity itself. Hydroxides have, to create phenoxide salts as the first product. These are better nucleophiles than their progenitor, and also base-destabilised nitro compounds. Result heat and probable loss of control. As it nears its boiling point DMSO also becomes susceptible to exothermic breakdown, initially to methanethiol and formaldehyde. Methanethiolate is an even better nucleophile than a phenoxide and also a fairly proficient reducer of nitro-groups, while formaldehyde condenses with phenols under base catalysis in a reaction which has itself caused many an industrial runaway and explosion. There is thus a choice of routes to disaster. Industrial scale nucleophilic substitution on chloro-nitroaromatics has previously demonstrated considerable hazard in presence of water or hydroxide, even in solvents not themselves prone to exothermic decomposition [2],... 

Incidents of several different types have arisen from reactions involving neutralisation of an acid with a base where the exotherm (57.3 kJ/equivalent for strong acid—strong base reactions) has not occurred smoothly over an extended period, but has been sudden in effect for various reasons. Individually indexed neutralisation incidents are f Formaldehyde, Magnesium carbonate hydroxide, 0415 Potassium hydroxide, Acids, 4422 Sodium carbonate, 0549 Sulfuric acid, 4-Methylpyridine, 4473 Sulfuric acid, Diethylamine, 4473 2,4,6-Trichloro-l,3,5-triazine, 2-Ethoxyethanol, 1035 See related UNIT process or unit operation incidents... 

One obvious candidate for an electrophilic but non-enolisable compound is formaldehyde CH2=0 but it is simply too electrophilic to be well controlled. A trivial example is its reaction with acetaldehyde and hydroxide ion. The first aldol gives the expected product 43 but a second gives 44 and a third follows. Now hydroxide adds to another molecule of formaldehyde and delivers a hydride ion 45 in the Cannizzaro reaction (the other product is formate ion HCO2-) to give pentaerythritol 46, a useful compound in polymer chemistry for cross-linking but not much use to us. We need to moderate the unruly behaviour of this useful one-carbon electrophile. 

The first reported ferroceno heterocyclic compound of the type 1 was A-methyltetrahydropyridoferrocene (4). This compound was obtained from an anomalous Leuckart-Eschweiler-Clark reaction of 2-aminomethylferrocene (5 R = H), formaldehyde, and formic acid,4 although the structure 4 was not immediately recognized for this compound.5-8 The heterocyclic compound 4 can be used as an entry to 1,2-disubstituted ferrocenes since on reaction with potassium amide in liquid ammonia7 or with potassium hydroxide in methanol9 its... 

The compound appears as large yellow crystals, m.p. 111°. With sodium hydroxide in alcohol an intense violet coloration is produced. With formaldehyde and sodium hydroxide in aqueous solution S7NCH2OH (m.p. 110.5°) is formed. With acetyl chloride in chloroform in the presence of pyridine reaction occurs at 0° with the formation of yellow needles of S7NCOCH3 (m.p. 104.4°). ... 

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. 

Cross Cannizzaro reactions. Under solvent-free conditions the microwave irradiation of a mixture of aldehydes with formaldehyde and barium hydroxide gives alcohols. 

Preparation. Imidazole can be prepared by a remarkable method discovered by Maquenne D-tartaric acid is converted into the dinitrate, and the ester on reaction with ammonium hydroxide and formaldehyde affords imidazole-4,5-dicarboxylic acid, which is decarboxylated to the parent heterocycle. Diketosuccinic... 

In contrast to aliphatic alcohols, which are mostly less acidic than phenol, phenol forms salts with aqueous alkali hydroxide solutions. At room temperature, phenol can be liberated from the salts even with carbon dioxide. At temperatures near the boiling point of phenol, it can displace carboxylic acids, e.g. acetic acid, from their salts, and then phenolates are formed. The contribution of ortho- and -quinonoid resonance structures allows electrophilic substitution reactions such as chlorination, sulphonation, nitration, nitrosation and mercuration. The introduction of two or three nitro groups into the benzene ring can only be achieved indirectly because of the sensitivity of phenol towards oxidation. Nitrosation in the para position can be carried out even at ice bath temperature. Phenol readily reacts with carbonyl compounds in the presence of acid or basic catalysts. Formaldehyde reacts with phenol to yield hydroxybenzyl alcohols, and synthetic resins on further reaction. Reaction of acetone with phenol yields bisphenol A [2,2-bis(4-hydroxyphenyl)propane]. 

Butlerov found out that in alkaline medium (calcium hydroxide), formaldehyde HCHO polymerizes to form about 20 different sugars as racemic mixtures, Butlerov 1861. The reaction requires a divalent metal ion. Breslow found a detailed mechanism of reaction that explains the reaction products, (Breslow 1959). He found that glycol-aldehyde is the first product that is subsequently converted into glyceral-dehyde (a triose), di-hydroxy-acetone, and then into various other sugars, tetrose, pentose, and hexose. The formose reaction advances in an autocatalytic way in which the reaction product is itself the catalyst for that reaction with a long induction period. The intermediary steps proceed via aldol and retro-aldol condensations and, in addition, keto-enol tautomerizations. It remains unexplained how the phosphorylation of 3-glyceraldehyde leads to glycral-3-phosphate (Fig. 3.6). Future work should study whether or not ribozymes exist that can carry out this reaction in a stereo-specific way. 

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