Formaldehyde reaction order

Base-catalyzed phenol-formaldehyde reactions exhibit second-order kinetics [Eq. (5)]. Several alkylphenols such as cresols also follow this rate equation ... 

The reaction conditions, formaldehyde-to-phenol ratios, and concentration and type of catalyst govern the mechanisms and kinetics of resole syntheses. Higher formaldehyde-to-phenol ratios accelerate the reaction rates. This is to be expected since phenol-formaldehyde reactions follow second-order kinetics. Increased hydroxymethyl substitution on phenols due to higher formaldehyde compositions also leads to more condensation products.55... 

The model-based controller-observer scheme requires to solve online the system of differential equations of the observer. The phenol-formaldehyde reaction model is characterized by 15 differential equations, and it is, thus, unsuitable for online computations. To overcome this problem, one of the reduced models developed in Sect. 3.8.1 can be adopted. In order to be consistent with the general form of nonchain reactions (2.27) adopted to develop the controller-observer scheme, the reduced model (3.57) with first-order kinetics has been used to design the observer. The mass balances of the reduced model are given by... 

The transformation of VIII/3 to VIII/4 is called a fragmentation1 [3] [4]. As in the aldol reaction the reverse version of the fragmentation also is known (VIII/4 — VIII/3). An example of this reaction type is the so-called Prins reaction the acid catalyzed (base catalysis is also possible) addition of an olefin to formaldehyde in order to get a 1,3-diol. Further examples are known in the field of transannular reactions in medium-sized rings [5],... 

The last decade has seen quite remarkable advances in our knowledge of the structure and properties of the proanthocyanidins. Viscosity measurements were made of solutions of procyanidins isolated from Theobroma cacao and Chaenomeles speciosa with number-average degrees of polymerization of 6.1 and 11.8, respectively, in water and 1% sodium hydroxide at 25 °C. Procyanidins are apparently completely crosslinked by formaldehyde up to a chain length of 6 units, but few units are crosslinked in polymeric procyanidins. The second order rate constants observed for the formaldehyde reaction with catechin or epicatechin are approximately six times higher than that observed for the C. speciosa polymer. 

The second kind of polycondcnsalion based on the Mannich reaction includes monomers of type A-B (384, Fig. 152), requiring equimolar amounts of formaldehyde in order to produce the polymeric derivatives 385. 

Since the kinetic experiments within the NiCr catalyst showed that formaldehyde retarded the hydrogenation kinetics of the aldol, especially at higher temperatures, pseudo-first order kinetics could not be applied for the aldol hydrogenation as illustrated in Figure 7. The logarithmic test plots are bent upwards, which indicate that the reaction order is less than one with respect to aldol. 

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. 

The kinetics of the urea-formaldehyde reaction have been investigated by de Jong and de Jonge. It is an equilibrium reaction with a second-order reaction forward and first Order in reverse. The equilibrium is far to the right. 

Figure 6, which is a plot of the formaldehyde reaction-rate versus the concentration of calcium hydroxide in the reactor (rather than its concentration in the combined feed), shows the reaction rate to be independent of formaldehyde feed-rate at intermediate levels of conversion. At these conversion levels, the formaldehyde reaction-rate is first-order in calcium hydroxide, and zero-order in concentrations of formaldehyde and products, or... 

In order to eliminate Cannizzaro effects from the data for the formaldehyde reaction-rate, the formose reaction-rate, Tf was defined [total... 

Second-order kinetics were also established for base-catalyzed formaldehyde reactions with m-cresol " and p-cresol. However, Fitzgerald and Martin reported fractional orders for reactions of 2,3,4,5-tetramethylphenol and 2,6-xylenol. ... 

If one wishes to stndy a reaction theoretically, the most simple example is usually where one starts, which wonld be with the ammonia/formaldehyde reaction in the present case. Bnt when stndying a reaction experimentally, it is often convenient to start with much more complicated examples. The latter approach was followed historically, and we will discnss it here in historical order. 

Freeman and Lewis [23] published one of the first complete kinetic investigations of phenol with formaldehyde. The hydroxymethylation at 30°C was followed by analysis using quantitative paper chromatography with detection of five products (2-hydroxymethylphenol, 4-hydroxymethyl-phenol, 2,4-dihydroxymethylphenol, 2,6-dihydroxymethylphenol, and 2,4,6-trihydroxymethylphenol). More recently, Zavitsas and Beaulieu [24] used GLC to investigate the kinetics of the phenol-formaldehyde reaction using only catalytic amounts of base and at pH ranges where the second-order rate expression was shown to be valid. 

In a 500 ml. conical flask place 50 ml. of glachtl acetic acid, 25 ml. of 40 per cent, formaldehyde solution (formalin) and 20 g. of phenol. Wrap a cloth or towel loosely around the neck and opening of the flask. Pass dry hydrogen chloride gas (Section 11,48,1) into the mixture. Within 5 minutes, a large mass of pink plastic is formed the reaction is sometimes very vigorous. The yield is 36 g. It is frequently necessary to break the flask in order to remove the product completely for this reason a beaker, or metal flask or beaker, is preferable. 

The yields of this reaction are typically 40—80%. C-nmr studies (41) indicate that the reaction is a second-order process between polyacrylamide and dim ethyl am in om eth an ol, which is one of the equiUbrium products formed in the reaction between formaldehyde and dimethylamine [124-40-3] C2H2N. The Mannich reaction is reversible. Extensive dialysis of Mannich polyacrylamides removes all of the dimethyl aminomethyl substituents (42). 

The exact order of the production steps may vary widely in addition, some parts of the process may also vary. Metal formate removal may occur immediately after the reaction (62) following formaldehyde and water removal, or by separation from the mother Hquor of the first-stage crystallization (63). The metal formate may be recovered to hydroxide and/or formic acid by ion exchange or used as is for deicing or other commercial appHcations. Similarly, crystallization may include sophisticated techniques such as multistage fractional crystallization, which allows a wider choice of composition of the final product(s) (64,65). 

At ordinary temperatures, formaldehyde gas is readily soluble in water, alcohols, and other polar solvents. Its heat of solution in water and the lower ahphatic alcohols is approximately 63 kJ/mol (15 kcal/mol). The reaction of unhydrated formaldehyde with water is very fast the first-order rate constant... 

Methanol can be converted to a dye after oxidation to formaldehyde and subsequent reaction with chromatropic acid [148-25-4]. The dye formed can be deterruined photometrically. However, gc methods are more convenient. Ammonium formate [540-69-2] is converted thermally to formic acid and ammonia. The latter is trapped by formaldehyde, which makes it possible to titrate the residual acid by conventional methods. The water content can be determined by standard Kad Eischer titration. In order to determine iron, it has to be reduced to the iron(II) form and converted to its bipyridyl complex. This compound is red and can be determined photometrically. Contamination with iron and impurities with polymeric hydrocyanic acid are mainly responsible for the color number of the merchandized formamide (<20 APHA). Hydrocyanic acid is detected by converting it to a blue dye that is analyzed and deterruined photometrically. 

The nitro alcohols available in commercial quantities are manufactured by the condensation of nitroparaffins with formaldehyde [50-00-0]. These condensations are equiUbrium reactions, and potential exists for the formation of polymeric materials. Therefore, reaction conditions, eg, reaction time, temperature, mole ratio of the reactants, catalyst level, and catalyst removal, must be carefully controlled in order to obtain the desired nitro alcohol in good yield (6). Paraformaldehyde can be used in place of aqueous formaldehyde. A wide variety of basic catalysts, including amines, quaternary ammonium hydroxides, and inorganic hydroxides and carbonates, can be used. After completion of the reaction, the reaction mixture must be made acidic, either by addition of mineral acid or by removal of base by an ion-exchange resin in order to prevent reversal of the reaction during the isolation of the nitro alcohol (see Ion exchange). 

A melamine laminating resin used to saturate the print and overlay papers of a typical decorative laminate might contain two moles of formaldehyde for each mole of melamine. In order to inhibit crystallization of methylo1 melamines, the reaction is continued until about one-fourth of the reaction product has been converted to low molecular weight polymer. A simple deterrnination of free formaldehyde may be used to foUow the first stage of the reaction, and the build-up of polymer in the reaction mixture may be followed by cloud-point dilution or viscosity tests. 

Stepwise thermal- or base-eatalysed hydrolytic depolymerisation initiated from the hemi-formal chain end with the evolution of formaldehyde. The main reasons for end-capping and copolymerisation mechanisms described above are carried out in order to minimise this reaction. 

In general, the reaction between a phenol and an aldehyde is classified as an electrophilic aromatic substitution, though some researchers have classed it as a nucleophilic substitution (Sn2) on aldehyde [84]. These mechanisms are probably indistinguishable on the basis of kinetics, though the charge-dispersed sp carbon structure of phenate does not fit our normal concept of a good nucleophile. In phenol-formaldehyde resins, the observed hydroxymethylation kinetics are second-order, first-order in phenol and first-order in formaldehyde. 

The study of PF polymerization is far more difficult than that of methylolation due to the increased complexity of the reactions, the intractability of the material, and a resulting lack of adequate analytical methods. When dealing with methylolation, we saw that every reactive ring position had its own reaction rate with formaldehyde that varied with the extent of prior reaction of the ring. Despite this rate sensitivity and complexity, all reactions kinetics were second-order overall, first-order in phenol reactive sites and first-order in formaldehyde. This is not the case with the condensation reactions. 

Alkaline co-condensation to yield commercial resins and the products of reaction obtained thereof [93,94] as well as the kinetics of the co-condensation of mono methylol phenols and urea [104,105] have also been reported [17]. Model reactions in order to prove an urea-phenol-formaldehyde co-condensation (reaction of urea with methylolphenols) are described by Tomita and Hse [98,102, 106] and by Pizzi et al. [93,104] (Fig. 1). 

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