Methylene glycol

The materials we shall discuss are all polymers of formaldehyde which may be viewed as methylene glycol in the presence of water ... 

FLUORINECOMPOUNDS,ORGANIC - FLUORINATED ALIPHATIC COMPOUNDS] (Vol 11) Methylene glycol [463-57-0]... 

Formaldehyde is produced and sold as water solutions containing variable amounts of methanol. These solutions are complex equiUbrium mixtures of methylene glycol, CH2(OH)2, poly(oxymethylene glycols), and hemiformals of these glycols. Ultraviolet spectroscopic studies (13—15) iadicate that even ia highly concentrated solutions the content of unhydrated HCHO is <0.04 wt%. 

Aqueous Formaldehyde. Water solutions of formaldehyde consist mainly of telomers of methylene glycol having <100 ppm of the formaldehyde as CH2O (5). Alcohols form hemiformals with aqueous formaldehyde according to the following, where n = 1,2,3, etc. 

Alkaline catalysts are also effective in the polymeri2ation—depolymeri2ation of methylene glycol. The mechanism of the formaldehyde addition to the phenolate is still not completely understood. The most likely mechanism involves the contribution of phenol hemiformals (10) (5). 

Rate studies show that base-cataly2ed reactions are second order and depend on the phenolate and methylene glycol concentrations. The most likely path involves a nucleophilic displacement by the phenoxide on the methylene glycol (1), with the hydroxyl as the leaving group. In alkaline media, the methylolated quinone intermediate is readily converted to the phenoxide by hydrogen-ion abstraction (21). 

Methyidichloroarsine Methylene glycol dinitrate Methyl ethyl ketone peroxide, >50% alpha-Methylglucoside tetranitrate alpha-Methylglycerol trinitrate Methyl nitramine (dry) metal salts of Methyl nitrate Methyl nitrite... 

Zavitsas et al. added terms for the extent of hemiformal and paraformaldehyde formation. Hemiformal formation slows the methylolation reaction as does the presence of paraformaldehyde. They report that only monomeric methylene glycol appears to methylolate. They point out that the terms for the two polyoxy-methylene species partially cancel one another, as depolymerization of paraformaldehyde naturally occurs while hemiformal formation is increasing due to methylolation. They observe that hemiformals form only on the methylolphenol hydroxyls and not on the aromatic hydroxyl. They calculate that the average number of methoxy groups involved in each of the hemiformals is about two in addition to the original methylol. There is no selectivity for ortho versus para positions in hemiformal formation. 

Zavitsas et al. take the alkalinity of the reaction mixture and the relative acidity of the various phenol derivatives into account in their study. Their rate scheme is corrected for the acidity of each individual species as it forms. They state that alkalinity has no appreciable effect on the availability of methylene glycol. 

Trimethylenc chlorohydrin has been prepared from tri-methylene glycol by the action of dry hydrogen chloride... 

In addition to Cyclonite, a nitrate of methylene glycol is also formed as a result of the cleavage of one of the three linkages between each nitrogen and carbon atom 0N02... 

Hydrogenation, of gallic add with rhodium-alumina catalyst, 43, 62 of resorcinol to dihydroresorcinol, 41,56 Hydrogen peroxide, and formic acid, with indene, 41, 53 in oxidation of benzoic add to peroxy-benzoic add, 43, 93 in oxidation of ieri-butyl alcohol to a,a/r, a -tetramcthyltetra-methylene glycol, 40, 90 in oxidation of teri-butylamine to a,<, a, a -tetramethyltetra-methylenediamine, 40, 92 in oxidation of Crystal Violet, 41, 2, 3—4... 

Novolacs are prepared with an excess of phenol over formaldehyde under acidic conditions (Fig. 7.6). A methylene glycol is protonated by an acid from the reaction medium, which then releases water to form a hydroxymethylene cation (step 1 in Fig. 7.6). This ion hydroxyalkylates a phenol via electrophilic aromatic substitution. The rate-determining step of the sequence occurs in step 2 where a pair of electrons from the phenol ring attacks the electrophile forming a car-bocation intermediate. The methylol group of the hydroxymethylated phenol is unstable in the presence of acid and loses water readily to form a benzylic carbo-nium ion (step 3). This ion then reacts with another phenol to form a methylene bridge in another electrophilic aromatic substitution. This major process repeats until the formaldehyde is exhausted. 

Similar ideas can be applied to formaldehyde oxidation. For bulk formaldehyde oxidation, we found predominant formic acid formation under current reaction conditions rather than CO2 formation. Hence, it cannot be ruled out, and may even be realistic, that formaldehyde is first oxidized to formic acid, which can subsequently be oxidized to CO2. The steady-state product distribution at 0.6 V is much more favorable for such a mechanism as in the case of methanol oxidation. On the other hand, because of the high efficiency of COad formation from formaldehyde, this process is likely to proceed directly from formaldehyde adsorption rather than via formation and re-adsorption of formic acid. Alternatively, the second oxygen can be introduced via formaldehyde hydration to methylene glycol, which could be further oxidized to formic acid and finally to CO2 (see the next paragraph). 

Hydroboration reactions are usually carried out in ether either in (C2H5)20, or in some higher molecular weight ether such as diglyme [(CH30CH2CH2)20, Methylene glycol di/nethyl ether]. 

Figure 12.2 Structural formulas of formaldehyde and its hydrate, methylene glycol.

Formaldehyde is usually described as a gas, but it also exists dissolved in water or other solvents. Because of very strong tendencies to hydrogen-bond, both formaldehyde and water combine avidly to make a hydrated compound called methylene glycol (Fig. 12.2). 

Much has been made about methylene glycol being the cause for formaldehyde s slow rate of fixation, succinctly expressed by Fox et al.7 Equilibrium between formaldehyde as carbonyl formaldehyde and methylene glycol explains most of the mystery of why formaldehyde penetrates rapidly (as methylene glycol) and fixes slowly (as carbonyl formaldehyde). Flowever, the equilibrium equation indicates the proportional amounts of carbonyl formaldehyde and methylene glycol, not the rate of conversion between the two... 

On Cu, the overall anodic reaction involving formaldehyde, or more correctly, the methylene glycolate anion may be depicted as ... 

It is seen that one electron is obtained for each methylene glycolate anion on Cu catalysts, although there is a possibility of obtaining two electrons if protons (or H2O in alkaline solution) were produced instead of H2 gas. The latter case is observed at Pd and Pt catalysts [38, 51, 53] ... 

Van den Meerakker [51] proposed a mechanism for methylene glycolate oxidation at Cu that included a step involving dehydrogenation of adsorbed methylene glycolate anion ... 

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