Formaldehyde oligomerization

Ferrocenylphosphine-gold complexes, 225 Formaldehyde oligomerization, 332 Formic acid, transfer hydrogenation, 123 Formulas, chiral compounds, xiii-xvii Four-dimensional chemistty. See Asymmetric catalysis... 

Llabres i Xamena FX, Otero Arean C, Spera S, Merlo E, Zecchina A. Formaldehyde oligomerization on silicalite an FTIR and NMR study. Catal Lett 2004 95 51-5. 

Resins. As mentioned above, both furfural and furfuryl alcohol are widely used in resin apphcations. Another resin former, 2,5-furandimethanol [1883-75-6] (BHME), is prepared from furfuryl alcohol by reaction with formaldehyde. It is usually not isolated because oligomerization occurs simultaneously with formation (competing reaction). Both the monomer and oligomers are very reactive owing to difuntionahty, and are used primarily as binders for foundry sand (72) and fiberglass insulation (147,148). 

For methylene diphenyl diisocyanate (MDI), the initial reaction involves the condensation of aniline [62-53-3] (21) with formaldehyde [50-00-0] to yield a mixture of oligomeric amines (22, where n = 1, 2, 3...). For toluene diisocyanate, amine monomers are prepared by the nitration (qv) of toluene [108-88-3] and subsequent hydrogenation (see Amines byreduction). These materials are converted to the isocyanate, in the majority of the commercial aromatic isocyanate phosgenation processes, using a two-step approach. 

Process parameters can be varied to change the MDA isomer distribution and oligomeric content of PMDA products. Generally, aniline to formaldehyde molar ratios of 2 to 5 are used. To increase the MDA content, higher ratios of aniline to formaldehyde are employed. Increasing the acid to aniline ratio also increases the 4,4 -MDA content of the diamine fraction. Historically, the polyurethane industry consumes as much of the 4,4 -MDI isomer as possible. Recently, however, there has been an increasing demand for higher 2,4 -MDI and 2,4 -PMDI products to be used as replacements for... 

The cationic polymerization of cardanol under acidic conditions has been referred to earlier [170,171], NMR studies [16] indicated a carbonium ion initiated mechanism for oligomerization. PCP was found to be highly reactive with aldehydes, amines, and isocyates. Highly insoluble and infusible thermoset products could be obtained. Hexamine-cured PCP showed much superior thermal stability (Fig. 12) at temperatures above 500°C to that of the unmodified cardanol-formaldehyde resins. However, it was definitely inferior to phenolic resins at all temperatures. The difference in thermal stability between phenolic and PCP resins could be understood from the presence of the libile hydrocarbon segment in PCP. 

Erker and co-workers in 1983 found that Cp2Zr(CO)2 (2) was formed, along with a mixture of other organozirconium products, when oligomeric bis(cyclopentadienyl)dihydridozirconium, (Cp2ZrH2), was stirred in toluene under 148 atm of CO at room temperature for 1 week. While Cp2Zr(CO)2 (2) could be isolated in 30% yield, the product of interest was a novel trimeric (7j2-formaldehyde)zirconocene complex (56). 

M. Otta, H.H. Fischer, M. Maiwald, K. Albert, and H. Hasse, Kinetics of oligomerization reactions in formaldehyde solutions NMR experiments up to 373K and thermodynamically consistent model, Chem. Eng. Process., 44, 653-660 (2005). 

While highly reactive formaldonitrone (3) was detected only recently, both the nitrosomethane (1) and the formaldehyde oxime (2) are also reactive compounds in the condensed phase 2 undergoes facile oligomerization , whereas 1 forms a dimer and isomerizes to 2 . Deprotonation of any of these isomers (1, 2, 3) would result in the corresponding simplest nitrosomethanide anion [H2C=N—O]. ... 

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. 

Template copolymerization seems to be applied to the synthesis of copolymers with unconventional sequences of units. As it was shown, by copolymerization of styrene with oligomers prepared from p-cresyl-formaldehyde resin esterified by methacrylic or acrylic acid - short ladder-type blocks can be introduced to the macromolecule. After hydrolysis, copolymer with blocks of acrylic or methacrylic acid groups can be obtained. Number of groups in the block corresponds to the number of units in oligomeric multimonomer. Such copolymers cannot be obtained by the conventional copolymerization. 

Oligomeric urea-formaldehyde resins prepared by Wright et al. (2) were as effective as surfactants in separating drill cuttings from oil drilling fluids. 

Munson (171) carried out experimental work on HCN in zeolites in parallel with the acetonitrile experiments. The results were consistent with oligomerization. Although this process by itself is less interesting from a catalytic standpoint, the oligomerization of HCN and its reaction with formaldehyde remain of interest in the study of prebiotic syntheses of monomers that may have combined to form the first self-replicating systems (172). 

These deviations from linearity indicate the existence of an oligomeric distribution of chiral ligands. Noyori proposed a rationale as follows Due to the different dissociability (stability) of homochiral and heterochiral dimer, the enantiopurity of the remaining reactive catalyst (monomer) is improved as compared with that of the submitted chiral ligand 6 (Scheme 9.5) [11]. Heterochiral dimer is thermodynamically more stable than homochiral dimer, which is consistent with Noyori s rationale mentioned above [12a]. An ab initio molecular orbital study was also reported in a simplified model reaction between formaldehyde and dimethylzinc catalyzed by achiral 2-aminoethanol [12b]. 

For a given nucleophile the equilibrium lies farther on the product side the smaller the substituents R1 and R2 of the carbonyl compound are (Figure 9.1). Large substituents R1 and R2 inhibit the formation of addition products. This is because they come closer to each other in the addition product, where the bonds to R1 and R2 are closer than in the carbonyl compound, where these substituents are separated by a bond angle of about 120°. Formaldehyde is the sterically least hindered carbonyl compound. In H20 this aldehyde is present completely as dihydroxymethane, and anhydrous formaldehyde is exists completely as polymer. In contrast, acetone is so sterically hindered that it does not hydrate, oligomerize, or polymerize at all. 

Some aldehydes oligomerize in the presence of acids. The polymerization of formaldehyde (formation of H see Figure 9.10) as well as that of aldehydes with strong electronegative sub-... 

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