Formaldehyde depolymerization

Trioxane, the cyclical trimer of formaldehyde, depolymerizes in the presence of acid catalysts. Batch test with 8NH2SO4 gave the conversions at different temperatures shown in Table 1.8 [11]. 

This is the least desirable of all three processes [What do you mean by that This is really easy to do And the yield are fine ]. The yields are lower than the two rearrangements, and it requires substantial labor to get a decently pure product. Not "labor" as In difficult but "labor" as in a lot of it. I would suggest this only for those who have a large supply of Formaldehyde available to them (note - N. Coffey found formaldehyde at Home Depot - look for "Mildewcide" and dissolve it in enough water to make a 37% solution to depolymerize the paraformaldehyde). 

Place 3 3oz packets of Mildewcide into a 1L flask with an electric heating mantle and cork in the neck connected to a gas bubbler immersed in at least 550mL of distilled water. Heat the paraformaldehyde (what is in the Mildewcide) to between 180-200C (a temp, regulator is absolutely necessary for this step or use a silicone oil bath). The paraformaldehyde will depolymerize making formaldehyde gas in about 91% yield. Alternatively, the gas can be bubbled through the Ammonia solution directly (only for the brave ). If the Formaldehyde solution will not be used immedi-... 

Paraformaldehyde [30525-89-4] is a mixture of polyoxymethylene glycols, H0(CH20) H, with n from 8 to as much as 100. It is commercially available as a powder (95%) and as flake (91%). The remainder is a mixture of water and methanol. Paraformaldehyde is an unstable polymer that easily regenerates formaldehyde in solution. Under alkaline conditions, the chains depolymerize from the ends, whereas in acid solution the chains are randomly cleaved (17). Paraformaldehyde is often used when the presence of a large amount of water should be avoided as in the preparation of alkylated amino resins for coatings. Formaldehyde may also exist in the form of the cycHc trimer trioxane [110-88-3]. This is a fairly stable compound that does not easily release formaldehyde, hence it is not used as a source of formaldehyde for making amino resins. 

The polymer also can be made from trioxane (the trimer of formaldehyde), usually as a copolymer with ethylene oxide. The —CH2CH2— fragments in the copolymer chain prevent depolymerization acetal copolymer was developed by Celanese (10). 

Zavitsas et al. account for the effects of water in their calculations. Water promotes depolymerization of the paraformaldehyde as well as the hemiformals. Their modifications correct for the apparent reduction in methylolation rate as the extent of reaction proceeds, in that the hemiformals remove formaldehyde reactivity from the reaction mixture. Their rate constants look large because they are written for phenate concentrations rather than phenol and because of the formaldehyde equilibrium adjustments. They note that unsalted phenol is a by-... 

While starches are commonly used, they are relatively poor viscosifiers. Acids and bacterial enzymes readily attack the acetal linkages resulting in facile depolymerization. Both formaldehyde and isothiazolones have been used as starch biocides (17). Development of improved high temperature water viscosifiers for drilling and other oil field applications is underway. For the... 

Formaldehyde solutions prepared by dissolving and depolymerization of paraformaldehyde (a homopolymer of formaldehyde with empirical formula HO (CH20)nH, where n > 6) are free of admixtures of methanol and formic acid. Depolymerized paraformaldehyde is useful in enzyme histochemistry, when the preservation of the enzyme activity is of crucial importance, but it has no advantage over formalin solutions routinely used in pathology and in immunohistochemistry. 

The industrial synthesis of polyformaldehyde [poly(oxymethylene)] occurs by anionic polymerization of formaldehyde in suspension. For this the purification and handling of monomeric formaldehyde is of special importance since it tends to form solid paraformaldehyde. After the polymerization the semiacetal end groups have to be protected in order to avoid thermal depolymerization (Example 5-13). This is achieved by esterfication with acetic anhydride (see Example 5-7). As in the case of trioxane copolymers (see Sect. 3.2.3.2) the homopolymers of formaldehyde find application as engineering plastics. 

The concept of a (bound) formaldehyde intermediate in CO hydrogenation is supported by the work of Feder and Rathke (36) and Fahey (43). Experiments under H2/CO pressure at 182-220°C showed that paraformaldehyde and trioxane (which depolymerize to formaldehyde at reaction temperatures) are converted by the cobalt catalyst to the same products as those formed from H2/CO alone. The rate of product formation is faster than in comparable H2/CO-only experiments, and product distributions are different, apparently because secondary reactions are now less competitive. However, Rathke and Feder note that the formate/alcohol ratio is similar to that found in H2/CO-only reactions (36). Roth and Orchin have reported that monomeric formaldehyde reacts with HCo(CO)4 under 1 atm of CO at 0°C to form glycolaldehyde, an ethylene glycol precursor (75). The postulated steps in this process are shown in (19)—(21), in which complexes not observed but... 

Polymers of formaldehyde were found recently in interstellar space by N. Wickramasinghe [Nature, 252, 462 (1974)]. It is well known that polyformaldehyde is thermodynamically unstable already at not very high temperatures (close to room temperature), but it should be stable versus depolymerization near absolute zero. Therefore the formation of poly-oxymethylene near absolute zero is not a thermodynamic but a kinetic problem. 

Rapid and uniform fixation throughout the tissue block with formaldehyde can be obtained at high temperatures, for example, in a microwave oven. Such temperatures enhance the speed and extent of formaldehyde reaction with proteins by dissociating the methylene glycol to formaldehyde as well as by depolymerizing the oligomers of methylene glycol (Boon et al., 1988). 

Resorcinol differs from other phenols in that it reacts readily with formaldehyde under neutral conditions at ambient temperature. To make stable adhesives, which can be cured at the point of use, they are prepared with less than a stoichiometric amount of formaldehyde. About two thirds of a mole of formaldehyde for each mole of resorcinol will give a stable resinous condensation product. The resin is formed into a liquid of convenient solids content and viscosity. Such solutions have infinite stability when stored in closed containers. Glue mixes formed at the point of use from these solutions, on addition of paraformaldehyde-containing hardeners, will have a useful life of several hours due to two principal factors (1) the paraformaldehyde depolymerizes to supply monomeric formaldehyde at a slow rate, as determined by the pH (2) the availability of the formaldehyde is also controlled by the kind and amount of alcohol in the solvent. Formaldehyde reacts with the alcohol to form a hemiacetal. This reaction is reversible and forms an equilibrium which exerts further control on the availability of the formaldehyde. 

Formaldehyde seems to be the obvious product of depolymerization of monosaccharides. According to Berger et al.iss details of the process are as follows. 

Figure 9.10 presents the mechanism of the polymerization of formaldehyde starting from anhydrous formaldehyde and formaldehyde hydrate. In addition, a reaction path is shown that also connects trimeric formaldehyde ( trioxane, F) with paraformaldehyde (H). In practice, though, this reaction path is only taken in the reverse direction, upon heating (entropy gain ) of paraformaldehyde in aqueous acid as a depolymerization of H —> F. 

Some hetero double bond systems have been shown to enter [3 + 2] cycloaddition reactions with the mesoionic 1,3-dithiolones. Thus, the mesoionic 1,3-dithiolones (2) react with formaldehyde, prepared in situ by depolymerization of paraformaldehyde, with regiospecific formation of the 2-oxa-6,7-dithiabicyclo[2.2.1]heptanone derivatives (131). The corresponding reaction of (2) with the N=N double bond of dimethyl azodicarboxylate proceeds via cycloaddition yielding (132), and a similar reaction takes place between (2) and 4-phenyl-l,2,4-triazoline-3,5-dione (78CB3171). 

Tn the cationic polymerization and copolymerization of trioxane in the - melt or in solution, an induction period usually exists, during which no solid polymer is formed and the reaction medium remains clear. Nevertheless, reactions are known to occur during this period. By using BF3 or an ether ate as catalyst, in homopolymerization, Kern and Jaacks (I) reported the formation of formaldehyde via depolymerization of polyoxymethylene cations. 

Cleavage of formaldehyde from the active centers and polymerization of formaldehyde at the same cationic chain ends (polymerization-depolymerization equilibrium of formaldehyde) (9). 

On the other hand, no difference in equilibrium concentration is expected between Models C and B. In the latter only the "dead chain segments are crystallized while the cationic active centers, at which depolymerization and polymerization of formaldehyde takes place, are in solution. 

Dioxolane was also formed in the absence of trioxane when the soluble copolymer was simply dissolved in a 0.03M solution of SnCl4 in methylene dichloride at 30°C. (conditions similar to those of the copolymerization in Figure 3). Within one hour half of the soluble copolymer was depolymerized under formation of dioxolane monomer and formaldehyde. 

One of the most prominent features in the heterogeneous copolymerization of trioxane is the occurrence of two different kinds of active centers—dissolved and crystalline copolymer cations. They have different copolymer reactivity ratios and different tendencies to depolymerize, i.e., different formaldehyde equilibrium concentrations. At first the formation of soluble copolymer with high dioxolane content did not raise much hope for obtaining a crystalline copolymer of good thermal stability from trioxane and dioxolane but the gradual depolymerization of the soluble copolymer proved to be a useful side reaction which greatly improved the situation. Eventually, the entire complicated process turned out to be quite favorable for the formation of a stable crystalline copolymer with the desired random distribution. 

The institution of fractionated or chemically modified lignin for part or all of the phenol in the synthesis of phenol-formaldehyde resins. This would particularly include the newer forms of lignin recovered with minimum structural alteration and also those representing virtually complete depolymerization to phenylpropane units. 

The details of the commercial preparation of acetal homo- and copolymers are discussed later. One aspect of the polymerization so pervades the chemistry7 of the resulting polymers that familiarity with it is a prerequisite for understanding the chemistry of the polymers, the often subtle differences between homo- and copolymers, and the difficulties which had to be overcome to make the polymers commercially useful. The ionic polymerizations of formaldehyde and trioxane are equilibrium reactions. Unless suitable measures are taken, polymer will begin to revert to monomeric formaldehyde at processing temperatures by depolymerization (called unzipping) which begins at chain ends. 

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