Formaldehyde condensations estimation

Naphthalenesulfonic Acid—Formaldehyde Condensates. The sodium salts of the condensation products of naphthalenesulfonic acid with formaldehyde constitute an important class of compounds which are mainly used in the area of concrete additives (32,33), agricultural formulations, mbber formulations, and synthetic tanning agents. They are also used in photographic materials (34). Hampshire Chemical Co. and Henkel of America, Inc., are the largest suppHers of naphthalene sulfonate in concrete additives (superplasticizer) and reportedly hold 75—80% of this market. It was estimated that naphthalene sulfonate demand from U.S. producers would reach approximately... 

In 1994 estimated naphthalene consumption in western Europe and Japan for the production of alkylnaphthalene sulfonates, naphthalene sulfonate formaldehyde condensates, and synthetic tanning agents was... 

Marton and coworkers (27) estimated that only about 0.30 reactive aromatic sites are available for formaldehyde condensation per every C9 lignin unit of a softwood kraft lignin. Since this is only one-tenth as many available reactive sites as on phenol, it is not surprising that the utilization of lignin for commercial phenolic adhesives is extremely limited. 

Mapson (14) found that in solutions of pH 0.6 there is no significant condensation of formaldehyde with ascorbic acid. However, at this pH sulfides, sulfites, and thiol compounds combine readily with formaldehyde. He, therefore, proposed that the indophenol titration be carried out at pH 0.6 after the addition of formaldehyde to estimate ascorbic acid in the presence of the interfering sulfur compounds. 

Formaldehyde Condensation.—When an amino acid in neutral solution is mixed with excess of neutral formaldehyde solution, the mixture becomes acid, and can be titrated (Sorensen s reaction), thus affording an important method for the estimation of amino acids and ammonium salts. The mechanism of the change has been studied by Levy (1937). According to the older view, formaldehyde condenses with the amino group to form an unstable methylene-imino derivative, thereby destroying the basicity of the group. 

The compound (III) can however lose ethanol by an internal Claisen ester condensation (p. 264) to give the cyclohexane derivative (IV), which, being the ester of a (3-keto acid, in turn readily undergoes hydrolysis and decarboxylation to give 5,5Hiimethyl cyclohexan-i,3Hiione (V) or Dimedone, a valuable reagent for the detection and estimation of formaldehyde. 

By the mid-1990s world production of aminoplastics was estimated at about 6 000 000 t.p.a. of which more than 5 000 000 t.p.a. were urea-formaldehyde resins. The bulk of the rest were melamine-formaldehyde. Such bald statistics, however, disguise the fact that a considerable amount of aminoplastics used are actually co-condensates of urea, melamine and formaldehyde. 

Although the condensation of phenol with formaldehyde has been known for more than 100 years, it is only recently that the reaction could be studied in detail. Recent developments in analytical instrumentation like GC, GPC, HPLC, IR spectroscopy and NMR spectroscopy have made it possible for the intermediates involved in such reactions to be characterized and determined (1.-6). In addition, high speed computers can now be used to simulate the complicated multi-component, multi-path kinetic schemes involved in phenol-formaldehyde reactions (6-27) and optimization routines can be used in conjunction with computer-based models for phenol-formaldehyde reactions to estimate, from experimental data, reaction rates for the various processes involved. The combined use of precise analytical data and of computer-based techniques to analyze such data has been very fruitful. 

In order to estimate the kinetic parameters for the addition and condensation reactions, the procedure proposed in [11, 14] has been used, where the rate constant kc of each reaction at a fixed temperature of 80°C is computed by referring it to the rate constant k° at 80°C of a reference reaction, experimentally obtained. The ratio kc/k°, assumed to be temperature independent, can be computed by applying suitable correction coefficients, which take into account the different reactivity of the -ortho and -para positions of the phenol ring, the different reactivity due to the presence or absence of methylol groups and a frequency factor. In detail, the values in [11] for the resin RT84, obtained in the presence of an alkaline catalyst and with an initial molar ratio phenol/formaldehyde of 1 1.8, have been adopted. Once the rate constants at 80°C and the activation energies are known, it is possible to compute the preexponential factors ko of each reaction using the Arrhenius law (2.2). 

Both intermediates could conceivably decompose to MCPK by oxidative decarboxylation to give COx and water or by a concerted decarboxylation reaction to acetaldehyde starting from the first intermediate, or to formaldehyde starting from the second intermediate. However, neither intermediate, nor their dehydration products, nor acetaldehyde, formaldehyde, or CO were found even in trace quantities. Therefore, it appears that in this case as well the ketone is not being produced by an aldol reaction, but rather by a decarboxylative condensation reaction of the aldehyde and acetic acid, using oxygen from the surface as needed. When water was added, an increase in ketone formation was observed when comparing runs performed at the same CCald partial pressures. The reaction order for water was estimated to be 0.2. 

Experimental error was calculated by assuming measurement accuracies of 0.5 g (ca. 0.25%) for novolak weights and 2.0 g (ca. 0.25% this is a reasonable estimate of possible hang-up in the condenser) for distillate weights, and then solving for F P, amount of unreacted cresol, and DPn at these limits. Measurement errors for NMR determinations of copolymer composition and m-cresol 2,4-disubstitution were assumed to be 0.01, as determined in our earlier work. It is worth noting that a large error in the measurement of amount of formaldehyde reacted would render comparisons useless, since this is the independent variable for all of the calculations. 

A condensation reaction in which formaldehyde reacts with acetylacetone and ammonium ion to produce diacetyl lutidine which is coloured yellow. It is used in the estimation of triglycerides after the glycerol of the triglyceride molecule has been oxidized to formaldehyde. It can also be used for the estimation of uric acid in conjunction with the enzyme uricase. 

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