Solutions, formaldehyde Stabilizers

Although usually handled as an aqueous solution, formaldehyde cyanohydrin can be isolated in the anhydrous form by ether extraction, followed by drying and vacuum distillation (23). Pure formaldehyde cyanohydrin tends to be unstable especially at high pH. Small amounts of phosphoric acid or monochloroacetic acid are usually added as a stabiLher. Monochloroacetic acid is especially suited to this purpose because it codistiHs with formaldehyde cyanohydrin (24). Properly purified formaldehyde cyanohydrin has excellent stability (25). 

Resorcinol-formaldehyde (RF) solutions were prepared from resorcinol (Wako Pure Chemical Industries, Inc., research grade), formaldehyde (Wako Pure Chemical Industries, Inc., research grade, 37wt% formaldehyde stabilized with 8 wt% methanol), sodium carbonate (C) (Wako Pure Chemical Industries, Inc., research grade) and distilled water after ion exchange (W). The solutions were poured into glass tubes (iimer diameter 4 mm. 

Formaldehyde solution (Merck, Darmstadt, Germany Catalogue number 1.04003.1000 37% formaldehyde stabilized with about 10% methanol). 

The polymer solutions are stabilized with 500 ppm formaldehyde and kept practically oxygen free (<5 ppb O2). As the next figure shows (Fig. 8), clear viscosity differences arise even at a salinity of only 33 g/1 TDS (33,000 ppm) and reservoir temperatures of 195 °F (90 C). The viscosity values as measured at room temperature are expressed as a percentage of the original values before the temperature tests. 

Higher concentrations of formaldehyde are often supplied to customers using large quantities of the chemical, to reduce shipping costs and improve manufacturing efficiency. Heated storage tanks are required. For example, at 50% formaldehyde the solution must be kept at 55 C to avoid precipitation. A very highly concentrated form of formaldehyde stabilized with urea is also available. It is manufactured by Allied Chemical Co. and is known as UF Concentrate 85. The product contains 4.6 moles of formaldehyde for each mole of urea and is concentrated to 85% solids. It is convenient for... 

Experimental results (Fig. 7) showed conclusively that formaldehyde was primarily responsible for the stabilizing capability of commercially available formaldehyde solutions. Formaldehyde plus methanol was slightly better than formaldehyde alone, and formaldehyde alone was significantly more effective than methanol alone. 

Most formaldehyde producers recommend a minimum storage temperature for both stabilized and unstabilized solutions. Figure 3 is a plot of data (17,18,122,126) for uiiinhibited (<2.0 wt% methanol) formaldehyde. The minimum temperature to prevent paraformaldehyde formation in unstabilized 37% formaldehyde solutions stored for one to about three months is as follows 35°C with less than 1% methanol 21°C with 7% methanol 7°C with 10% methanol and 6°C with 12% methanol (127). 

However, a second mole of alcohol or hemiformal caimot be added at the ordinary pH of such solutions. The equiUbrium constant for hemiformal formation depends on the nature of the R group of the alcohol. Using nmr spectroscopy, a group of alcohols including phenol has been examined in solution with formaldehyde (15,16). The spectra indicated the degree of hemiformal formation in the order of >methanol > benzyl alcohol >phenol. Hemiformal formation provides the mechanism of stabilization methanol is much more effective than phenol in this regard. 

Aqueous formaldehyde, known as formalin, is usually 37 wt % formaldehyde, though more concentrated solutions are available. Formalin is the general-purpose formaldehyde of commerce suppHed unstabiLized or methanol-stabilized. The latter may be stored at room temperature without precipitation of soHd formaldehyde polymers because it contains 5 —10% methyl alcohol. The uiiinhibited type must be maintained at a temperature of at least 32°C to prevent the separation of soHd formaldehyde polymers. Large quantities are often suppHed in more concentrated solutions. Formalin at 44,... 

Sulfuric acid, formaldehyde, and hydrogen cyanide are pumped into a glass-lined mixer (mixer 1, Ml, of Fig. 13). Particular care is exercised so that the three charge operations are carried out in the order indicated above, to ensure the stability of the mixture at all times. In a separate segment of the plant, ethylenediamine (EDA) and dilute sodium hydroxide are charged and mixed in mixer 3 (M3 in Fig. 13). The solutions from mixer 1 and mixer 3 are pumped to the reactor (REACTOR, Rl, in Fig. 13). When the reaction is complete, the reaction mixture is tested for traces of hydrogen cyanide. Dilute solution of formaldehyde is prepared in mixture 2 and is added to the reaction mbrture, if there is any HCN present. 

Sometimes, extra chemicals are added to the main chemical as stabilizers. For example, formaldehyde is too reactive in its pure state to exist as formaldehyde for any length of time. It will dimerize or polymerize on standing. Formaldehyde is normally sold as a 40 vol% solution in water, with a methanol stabilizer (12 vol%) to slow down the polymerization. 

The experimental evaluation [4] of the stability of non-ionic surfactants (nonylphenol ethoxylates, NPEOs, and alcohol ethoxylates, AEOs) during sample storage showed that aqueous samples can be stored at 4°C without addition of any preservative only for a short time (a maximum of 5 days). The most often used preservative is formaline (1-8% (v/v) of 37% solution of formaldehyde in water). 

Oxazolidines are five-membered cyclic ft-Mannich bases, some of which have, indeed, been examined as potential produgs of /l-amino alcohols of medicinal relevance such as ephedrines and /3-blockers. For example, 3,4-dime-thyl-5-phenyloxazolidine (11.106), the oxazolidine of ephedrine (11.107) undergoes hydrolysis to ephedrine and formaldehyde slowly at pH 1 and 12, but very rapidly in the neutral pH range (tm < 1 min at 37°) [135], Interestingly, the equilibrium reached between the reactants and products of hydrolysis was markedly pH- and concentration-dependent. However, despite its poor stability in aqueous solution, the oxazolidine was delivered through human skin significantly faster than ephedrine when applied as 1% aqueous solutions of pH 7 - 11. The lower basicity of the oxazolidine (pKa 5.5) compared to that of ephedrine (pKa 9.6) may explain the efficient skin permeation. 

One of the major advantages of the metal oxide catalyst over that of the straight metal catalyst is the elimination of the need for a methanol recovery tower. The metal oxide catalysts result in not only high yields, but also very high conversion rates. Consequently, there is no need to recover the small amounts of methanol that remain unreacted. It becomes part of the aqueous formaldehyde solution and serves as a stabilizer for the system. By-products are CO, CO2, dimethyl ether, and formic acid. The process yields (the percent of the methanol that ends up in formaldehyde) are 95-98%. 

Formalin concentrations range from 37-56% by weight formaldehyde, the balance water, with or without stabilizer, bur most formalin merchant sales is shipped as 50% or stronger solutions. The higher concentrations generally require stabilizers. No hazardous shipping label is required. 

Note Formaldehyde solutions usually contain methanol as a stabilizer to inhibit polymerization. 

Vinyl substituted cyclic hemlamidals 2 and their Interconvertible acetal precursors (eg. acrylamldo-butyraldehyde dimethyl acetal 1) were Incorporated as latent crosslinkers and substrate reactive functional comonomers In solution and emulsion copolymers. Some use and applications data for copolymers prepared with these new monomers are presented. They show low energy cure potential, long shelf life and high catalyzed pot stability In solvent and aqueous media, good substrate reactivity and adhesion, and good product water and solvent resistance. They lack volatile or extractable aldehyde (eg. formaldehyde) components and show enhanced reactivity and hydrolytic stability with amines and diol functional substrates. 

Various metal oxides or silver metal are used as catalysts. Temperatures range from 450-900°C and there is a short contact time of 0.01 sec. Formaldehyde is stable only in water solution, commonly 37-56% formaldehyde by weight. Methanol (3-15%) may be present as a stabilizer. Formaldehyde in the pure form is a gas with a bp of - 21 °C but is unstable and readily trimerizes to trioxane or polymerizes to paraformaldehyde. 

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