Monomeric formaldehyde Preparation

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

Trioxane and Tetraoxane. The cycHc symmetrical trimer of formaldehyde, trioxane [110-88-3] is prepared by acid-catalyzed Hquid- or vapor-phase processes (147—151). It is a colorless crystalline soHd that bods at 114.5°C and melts at 61—62°C (17,152). The heats of formation are — 176.9 kJ/mol (—42.28 kcal/mol) from monomeric formaldehyde and —88.7 kJ/mol (—21.19 kcal/mol) from 60% aqueous formaldehyde. It can be produced by continuous distillation of 60% aqueous formaldehyde containing 2—5% sulfuric acid. Trioxane is extracted from the distillate with benzene or methylene chloride and recovered by distillation (153) or crystallization (154). It is mainly used for the production of acetal resins (qv). 

Monomer emulsion preparation, 76 286 Monomeric formaldehyde, properties of, 72 108t... 

Amino-substituted (Mannich base) polymers can be prepared by reacting amide-containing polymers with formaldehyde and a suitable amine. Sugiyama and Kamogawa (16) treated PAM in aqueous solution with excess paraformaldehyde (50°C, lh) followed by excess dimethylamine (50°C, lh). This procedure gave 68% conversion to amine. Schiller and Suen (9) used a similar procedure with monomeric formaldehyde and various amines, but with excess PAM. Muller et al. (17) prepared monomeric amines from... 

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. 

Substituted acrylic acids have been prepared by reaction of acid dianions with monomeric formaldehyde.48 A variation of the reaction permits in situ formation of formaldehyde from anions of methoxymethyl esters.49... 

When monomeric formaldehyde is needed, to react with a Grignard reagent, for example, it is prepared as needed by heating the polymer in order to depolymerize it. 

Ca. 5% excess dry paraformaldehyde added in small portions with occasional cooling to gently refluxing ethereal p-tolyllithium prepared from p-iodotoluene and lithium, stirring continued 10-15 min. p-methylbenzyl alcohol. Y 95%. — It is not necessary to prepare monomeric formaldehyde from the paraformaldehyde. F. e., also C-hydroxymethylation of acetylene derivatives, s. A. Schaap, L. Brandsma, and J. F. Arens, R. 8A, 1200 (1965). 

At the end of this decade, management authorized fundamental research into the preparation of pure monomeric formaldehyde and the study of its chemistry. 

The mono- and dianions of [ C2]acetylene, readily accessible by deprotonation with n-BuLi (1 equivalent) and MeLi (2.5 equivalents), respectively, can be trapped with monomeric formaldehyde to give [2,3- C2]propargyl alcohol in 40% yield and 2-[2,3- C2]butyne-l,4-diol in 72% yield. Both compounds may serve as valuable intermediates for the preparation of additional low-molecular weight building blocks and intermediates. [2,3- C2]propargyl alcohol, for example, can be reduced with aqueous CrCl2 to [2,3- C2]allyl alcohol, which was shown to be activated through tosylate formation toward nucleophilic displacement of the hydroxy function to produce radio-... 

Properties. Gamma-polyox miethylene is a colorless cn stalline product which decompt es on heating in the temperature range 160-210 C. The exact temperature of decomposition depends on the method of preparation and purification. It melts to a clear liquid at approximately 160-180°C. On % aporization, it depolymerizes to monomeric formaldehyde gas. The pohmer does not smell of formaldehyde and is insoluble in water and organic solvents. It is not affected by dilute alkalies, but dissolves with hydrolysis in acidic solutions when heat is appHed. 

The two key isocyanates that are used in the greatest volumes for polyurethane polymers are toluene diisocyanate (TDl) and methylene diphenyl diisocyanate (MDl). Both isocyanates are produced first by nitration of aromatics (toluene and benzene, respectively), followed by hydrogenation of the nitro aromatics to provide aromatic amines. In the case of MDl, the aniline intermediate is then condensed with formaldehyde to produce methylene dianiline (MDA), which is a mixture of monomeric MDA and an oligomeric form that is typical of aniline/formaldehyde condensation products [2]. The subsequent reaction of phosgene with the aromatic amines provides the isocyanate products. Isocyanates can also be prepared by the reaction of aromatic amines with dimethylcarbonate [3, 4]. This technology has been tested at the industrial pilot scale, but is not believed to be practiced commercially at this time. 

On a laboratory scale, one of the favored catalyst is the benzyl tri-n-butyl ammonium chloride (BTBAC). The most important reagent, a-chloroethyl chloroformate ( ACE-CI ), typically is isolated in 96% yield by stirring acetaldehyde with phosgene (1.1 eq.) neat for an hour in the presence of 3 mol. % BTBAC. Even chloromethyl chloroformate can be prepared using this process, but it is essential to introduce the monomeric gaseous formaldehyde into the... 

Donaruma and coworkers have studied copolymers of various sulfa drugs with formaldehyde or dimethylolurea. These copolymers often exhibited bacteriostatic activity and in some cases this activity level was higher than with the corresponding, monomeric, sulfa drug. The polymers often showed lower toxicity levels and, in general, the dimethylolurea derivatives showed higher bacteriostatic activity than did the formaldehyde derivatives. In earlier work, Donaruma and coworkers also prepared some antimalarlal, polymeric sulfomes and some bloactlve tropone derivatives (1,13). 

Monomeric partially and fully alkylated amino resins are prepared in two separate reaction steps. Hydroxymethylation is carried out under basic conditions to minimize self-condensation of the amino resin. The pH is then lowered by addition of a mineral acid and alkylation with methanol is carried out. To obtain monomeric amino resins, an excess of formaldehyde has to be used to assure a high level of hydroxymethylation and a low level of residual amide groups that would otherwise lead to polymer formation during the alkylation step. Since water removal by azeotropic distillation is not possible with methanol, a large excess of alcohol is required to achieve complete alkylation. After completion of alkylation the resin solution is neutralized water, alcohol, and residual formaldehyde are removed by vacuum distillation. The salt formed during neutralization is removed by filtration [2.154]. 

Phenolic resins contain oUgomeric and polymeric chains as well as monomeric methylol-phenols, free formaldehyde, and unreacted phenol. The contents of both monomers have to be minimized by the proper preparation procedure. Various preparation procedures are described in the Kterature and in patents [108-117],... 

Alkyl-2-cyanoacrylates can be prepared by several synthetic procedures. The only method of importance involves the Knoevenagel condensation of an alkylcyanoacetate with formaldehyde. As this is a base-catalysed reaction, the monomer is rapidly polymerized to give a low-molecular-weight poly(alkyl-2-cyanoacrylate). The resulting polymer is retropolymer-ized by heating under controlled conditions to yield monomeric cyanoacrylate (Scheme 1). 

In a typical process for the preparation of a methylated product, formalin is adjusted to pH 8 and melamine is added to give a melamine to formaldehyde ratio of 1 3.3 molar. The mixture is heated at 70°C for about 15 minutes until the melamine has completely dissolved. The solution is then either spray-dried or allowed to crystallize to give a solid composed essentially of monomeric methylolmelamines. This product is heated with about twice its weight of methanol and oxalic acid (0.5%) at 70°C until a clear solution is obtained. The solution is adjusted to pH 9 and concentrated to 80% solids under reduced pressure. The major component of this solution is the trimethyl ether of trimethy lolmelamine ... 

Another case occurs if there are two different templates connected by covalent bonds with monomeric units. In other words, it is a copolymerization of two different multimonomers, described in Reference 85. One multimonomer was prepared from poly(vinyl alcohol) and the another one from cresyl-formaldehyde resin (Scheme 12). 

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