Hydrated formaldehyde

Baker JR, Hew H, Fishman WH. The use of a chloral hydrate formaldehyde fixative solution in enzyme histochemistry. J. Histochem. Cytochem. 1958 6 244-250. 

D KIEs proved439 that in the oxidation of formaldehyde on a polycrystalline platinum electrode modified with Pb atoms and on pure platinum electrode, the cleavage of both OH and CH bonds and the abstraction of the hydrogen atom from an OH bond in hydrated formaldehyde are rate-determining on the Pt/Pb and on the Pt electrode, respectively. The ku/ku for the oxidation of formaldehyde at copper electrode (at pH 13, at 25 °C) depends on the electrode potential and reaches the highest value of 7 at low potentials and drops to about 2.5 at higher positive potentials440. 

Priha E, Liesivuori J, Santa H, et al. 1996. Reactions of hydrated formaldehyde in nasal mucus. Chemosphere 32 1077-1082. 

Urea-formaldehyde condensates show a surprisingly similar behavior to the lignin salts investigated by Terbilcox. The ability to produce a material such as UF concentrate demonstrates the solvent ability of hydrated formaldehyde. It is often seen that a fresh cook of a UF is clear, and will remain so for a short period of time. UF resins above a mole ratio of 1 2.5 (U F) are relatively easy to produce as a clear liquid. Typically resins which are produced at the very low F U ratios are the most difficult to make clear and are the least stable. 

One of the most important aqueous-phase reactions involving organic species is attack of the OH radical on hydrated formaldehyde... 

The OH radical in aqueous solution participates in a series of reactions both as a reactant and as a product. Its main sink for remote continental clouds is its reaction with hydrated formaldehyde discussed above. Other important sinks are reactions with hydrogen peroxide, formic acid, and S(IV). The main aqueous-phase sources of OH are reaction of 02 with 03 and photolysis of hydrogen peroxide. Secondary sources are photolysis of NO and oxidation of S(IV) with H02. 

The hydrated formyl radieal HC(0H)2 is a strong redueing speeies. It has been shown as an intermediate in the reaetion of hydrated formaldehyde with OH and is oxidized by H2O2 to form formic acid (or the formate anion, respectively). 

Note that some byproducts included on earlier WHO guideline lists (e.g., chloral and chloral hydrate, formaldehyde, trichloroacetonitrile) are not included as they are now considered to be present in drinking water at concentrations far below those considered to present a health risk. 

When aqueous solutions of formaldehyde are evaporated to dryness, a white crystalline solid (m.p. 121-123 C) known as paraformaldehyde is obtained. This comprises polyoxymethylene glycols formed by condensation of methylene glycol (hydrated formaldehyde see Section 8.3.2.) ... 

Table 19.2 lists the values for some representative hydration reactions. These equilibrium constants show the same trends found for the addition of HCN to a carbonyl group. Aldehydes with low molecular weights readily form hydrates. Formaldehyde is over 99% hydrated. Its hydrate is called formalin, a 37% by weight solution of formaldehyde in water that was used in the past to preserve biological specimens. Other aldehydes are substantially less hydrated. Ketones are normally hydrated less than 1%. The hydrates of aldehydes and ketones usually cannot be isolated and exist only in solution. 

---