Formaldehyde, acid catalyzed

PdCb-CuCb catalyzes the condensation of branched-chain alkenes with formaldehyde to give the l,3-dioxanes 96a and 96b (Prins reaction)[73]. The yields are much higher than in the conventional acid-catalyzed Prins reaction. 

An important synthetic process for forming a new carbon—carbon bond is the acid-catalyzed condensation of formaldehyde with olefins (Prins reaction) ... 

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). 

Methyl Isopropyl Ketone. Methyl isopropyl ketone [563-80-4] (3-methyl-2-butanone) is a colorless Hquid with a characteristic odor of lower ketones. It can be produced by hydrating isoprene over an acidic catalyst at 200—300°C (150,151) or by acid-catalyzed condensation of methyl ethyl ketone and formaldehyde to 2-methyl-l-buten-3-one, foUowed by hydrogenation to the product (152). Other patented preparations are known (155,156). Methyl isopropyl ketone is used as an intermediate in the production of pharmaceuticals and fragrances (see Perfumes), and as a solvent (157). It is domestically available from Eastman (Longview, Texas) (47). 

Pyrrole has been condensed under alkaline conditions with formaldehyde to give products of either N- or C-hydroxymethylation (Scheme 22). Although acid-catalyzed hydroxy-methylation is not a practical possibility, by addition of a reducing agent to the reaction mixture overall reductive alkylation can be achieved (Scheme 23). 

Practically all diaziridines (151) can be hydrolyzed by acids to a carbonyl compound and a hydrazine derivative. The only exceptions are diaziridines derived from formaldehyde, in which acid catalyzed N—N cleavage successfully competes with slow hydrolysis. Monoalkylhydrazines are formed in 80-95% yield, A/,A/ -dialkylhydrazines in 65-85% yield (B-67MI50800). 

All acid-catalyzed electrophilic substitution reactions are held by Treibs to occur by way of the distinct reactive species (23), thus the very greatly accelerated interaction of pyrrole and formaldehyde in acid solution involves attack of neutral formaldehyde on (23). Another example is the interaction of 2,3,4,6-tetramethylpyrrole with p-dimethylaminobenzaldehyde in acid solution, for which the following reaction (Scheme 2) is given,(23a) being presumably intended... 

DFT molecular dynamics simulations were used to investigate the kinetics of the chemical reactions that occur during the induction phase of acid-catalyzed polymerization of 205 [97JA7218]. These calculations support the experimental finding that the induction phase is characterized by the protolysis of 205 followed by a rapid decomposition into two formaldehyde molecules plus a methylenic carbocation (Scheme 135). For the second phase of the polymerization process, a reaction of the protonated 1,3,5-trioxane 208 with formaldehyde yielding 1,3,5,7-tetroxane 209 is discussed (Scheme 136). 

The acid-catalyzed addition of an aldehyde—often formaldehyde 1—to a carbon-carbon double bond can lead to formation of a variety of products. Depending on substrate structure and reaction conditions, a 1,3-diol 3, allylic alcohol 4 or a 1,3-dioxane 5 may be formed. This so-called Prins reaction often leads to a mixture of products. 

The Prins reaction often yields stereospecifically the and-addition product this observation is not rationalized by the above mechanism. Investigations of the sulfuric acid-catalyzed reaction of cyclohexene 8 with formaldehyde in acetic acid as solvent suggest that the carbenium ion species 7 is stabilized by a neighboring-group effect as shown in 9. The further reaction then proceeds from the face opposite to the coordinating OH-group " ... 

Phenol-formaldehyde resins are the oldest thermosetting polymers. They are produced by a condensation reaction between phenol and formaldehyde. Although many attempts were made to use the product and control the conditions for the acid-catalyzed reaction described by Bayer in 1872, there was no commercial production of the resin until the exhaustive work by Baekeland was published in 1909. In this paper, he describes the product as far superior to amber for pipe stem and similar articles, less flexible but more durable than celluloid, odorless, and fire-resistant. ° The reaction between phenol and formaldehyde is either base or acid catalyzed, and the polymers are termed resols (for the base catalyzed) and novalacs (for the acid catalyzed). 

The acid-catalyzed reaction occurs by an electrophilic substitution where formaldehyde is the electrophile. Condensation between the methylol groups and the benzene rings results in the formation of methylene bridges. Usually, the ratio of formaldehyde to phenol is kept less than unity to produce a linear fusible polymer in the first stage. Crosslinking of the formed polymer can occur by adding more formaldehyde and a small amount of hexamethylene tetramine (hexamine. 

The compound known as Ha emmm s ester is prepared by treatment of a mixture of formaldehyde and ethyl acetoacetate with base, followed by acid-catalyzed decarboxylation. 

Problem 31,11 Propose a mechanism to account for the formation of Bakelite from acid-catalyzed polymerization of phenol and formaldehyde. 

Acid-catalyzed aminomethylations of 5W-dibenz[/>,/]azepine (5) in ethanolic solution with formaldehyde and a secondary amine yield the 2-(aminoalkyl) derivatives, e.g. 6.186 If acetic acid is used as the solvent, however, then 2,8-bis(aminoaIkylatiou), e.g. formation of 7, results. 

Phenolic resins were discovered by Baeyer in 1872 through acid-catalyzed reactions of phenols and acetaldehyde. Kleeberg found in 1891 that resinous products could also be formed by reacting phenol with formaldehyde. But it was Baekeland who was granted patents in 1909 describing both base-catalyzed resoles (known as Bakelite resins) and acid-catalyzed novolac products.2... 

Phenol-formaldehyde reactions catalyzed by zinc acetate as opposed to strong acids have been investigated, but this results in lower yields and requires longer reaction times. The reported ortho-ortho content yield was as high as 97%. Several divalent metal species such as Ca, Ba, Sr, Mg, Zn, Co, and Pb combined with an organic acid (such as sulfonic and/or fluoroboric acid) improved the reaction efficiencies.14 The importance of an acid catalyst was attributed to facilitated decomposition of any dibenzyl ether groups formed in the process. It was also found that reaction rates could be accelerated with continuous azeotropic removal of water. 

Alkyl-substituted phenols have different reactivities than phenol toward reaction with formaldehyde. Relative reactivities determined by monitoring the disappearance of formaldehyde in phenol-paraformaldehyde reactions (Table 7.3) show that, under basic conditions, meta-cresol reacts with formaldehyde approximately three times faster titan phenol while ortho- and para-cresols react at approximately one-third the rate of phenol.18 Similar trends were observed for the reactivities of acid-catalyzed phenolic monomers with formaldehyde. 

Other cyclizations at phosphorus have been observed when certain phosphinates were used in the acid-catalyzed Mannich reaction. As observed previously with various phosphonous acid derivatives, reaction of aliphatic phosphinic acids with primary amines favored the formation of 2 1 adducts (73). Thus, glycine and other a-amino acids reacted under the typical conditions with excess formaldehyde and alkyl phosphonous acids to give the bis-phosphinylmethyl adducts 125. 

The reversible acid-catalyzed transacetalation of the cyclophane formal 3 has been shown to undergo a ring-fusion/ring-fission process to generate a mixture of polymer cyclic formaldehyde acetals by means of oxonium ion intermediates <06CEJ8566>. The stepwise... 

The same authors proposed a complex system for the electrochemically driven enzymatic reduction of carbon dioxide to form methanol. In this case, methyl viologen or the cofactor PQQ were used as mediators for the electroenzymatic reduction of carbon dioxide to formic acid catalyzed by formate dehydrogenase followed by the electrochemically driven enzymatic reduction of formate to methanol catalyzed by a PQQ-dependent alcohol dehydrogenase. With methyl viologen as mediator, the reaction goes through the intermediate formation of formaldehyde while with PQQ, methanol is formed directly [77],... 

The pH of a metalworking fluid must be kept above neutrality in order to prevent acid corrosion of the metal In vitro, acid catalyzed nitrosation is optimized at pH 3.5 (4 0) however, it has been shown that In the presence of other catalysts, aqueous solutions of amines and nitrite leads to significant yields of nitrosamines at room temperature over the pH range of 6.4 to 11.0 (41). Furthermore, C-nitro-containing, formaldehyde-releasing biocides, such as bronopol or tris nitro, exert their potential catalytic effect in alkaline solution. It would thus be desirable to determine the optimum pH for a metalworking fluid that would lead to the lowest concentration of nitrosamine possible. 

FIGURE 8.17 Preparation of Fmoc-A-methylamino acids by methylation of Fmoc-amino acids.90 Acid-catalyzed reaction of substrate with formaldehyde at elevated temperature with removal of water by azeotropic distillation produces the oxazolidinone, which is then opened and reduced to the A-methylated derivative. 

Figure 18. Diazonaphthoquinone-novolac resist. The novolac (Novolak) matrix resin is prepared by acid catalyzed copolymerization of cresol and formaldehyde. The base insoluble sensitizer, a diazohaphthoquinone, undergoes photolysis to produce a carbene which then undergoes Wolff rearrangement to form a ketene. The ketene adds water which is present in, the film, to form a base soluble, indenecarboxylic acid photoproduct.

Shackelford and co-workers studied the 1,2-addition of 2,2-dinitropropanol, 2,2,2-trinitroethanol, and 2-fluoro-2,2-dinitroethanol across the double bonds of vinyl ethers. These reactions are Lewis acid catalyzed because of the weak nucleophilic character of alcohols which contain two or three electron-withdrawing groups on the carbon p to the hydroxy functionality. Base catalysis is precluded since alkaline conditions lead to deformylation with the formation of formaldehyde and the nitronate salt. 

In 2008, the same group employed chiral dicarboxylic acid (R)-5 (5 mol%, R = 4- Bu-2,6-Me2-CgHj) as the catalyst in the asymmetric addition of aldehyde N,N-dialkylhydrazones 81 to aromatic iV-Boc-imines 11 in the presence of 4 A molecular sieves to provide a-amino hydrazones 176, valuable precursors of a-amino ketones, in good yields with excellent enantioselectivities (35-89%, 84-99% ee) (Scheme 74) [93], Aldehyde hydrazones are known as a class of acyl anion equivalents due to their aza-enamine structure. Their application in the field of asymmetric catalysis has been limited to the use of formaldehyde hydrazones (Scheme 30). Remarkably, the dicarboxylic acid-catalyzed method applied not only to formaldehyde hydrazone 81a (R = H) but also allowed for the use of various aryl-aldehyde hydrazones 81b (R = Ar) under shghtly modified conditions. Prior to this... 

Tetrahydro -/3-carboline has been prepared by the condensation of tryptamine with formaldehyde in the presence of sulfuric acid2 and has also been obtained as a by-product in the acid-catalyzed esterification of 1,2,3,4-tetrahydro-/3-carboline-1-carboxylic acid.3... 

Acid-Catalyzed Phenol-Formaldehyde Condensation (Novolaks)... 

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