Solutions, formaldehyde Commercial

The analyses can be carried out in the presence of /V-methy1o1 groups. On fabric, the formaldehyde bisulfite compound is decomposed by excess sodium carbonate and the Hberated sulfite is titrated with 0.1- or 0.01-N iodine solution (76). Commercial fabrics are seldom washed and dried before being used, and the free formaldehyde content may be between 50 and several hundred ppm, depending on finishing and storage conditions. 

In the determination of free formaldehyde in solution, eg, commercial reagents and pad bath formulation, the conditions of analysis allow hydrolysis of the /V-methy1o1 groups, usually between <1% and several percent. The NaOH formed is titrated with hydrochloric acid (82). Because of an incomplete reaction of sulfite with free formaldehyde, these low temperature methods (83) detect only 80—90% of the free formaldehyde present. Skill is important for correct results. 

Formaldehyde solution (40%). Commercial formaldehyde solution contains about 40 g HCHO per 100 ml. It normally contains some methanol as stabilizer. It has a characteristic, pungent odour. If kept in cold for longer times, solid paraldehyde separates from the solution. 

The three component coupling reactions also proceed smoothly in aqueous solution, and commercial aqueous formaldehyde solution can also be used directly (Eq. 11). 

Moreover, the three-component coupling reactions proceeded smoothly in aqueous solution, and commercial formaldehyde water solution could be used directly. Most lanthanide triflates tested were effective in the three-component coupling reactions (Table 23). These reactions provide very useful routes for the synthesis of pyridine and quinoline derivatives. 

In dilute alkaline solution formaldehyde is oxidized quantitatively to a formate by hydrogen peroxide. The percentage of formaldehyde in commercial formalin can be determined... 

Sc(OTf)3-catalyzed three-component coupling reactions of aldehydes, amines, and dienes have also been developed. In the presence of 10 mol % Sc(OTf)3 and magnesium sulfate, the reaction of benzaldehyde with aniline and Danishefsky s diene produces the tetrahydropyridine derivative in 83% yield, while the reaction with cyclopentadiene instead of Danishefsky s diene produces the tetrahydroquinoline derivative. Various combinations of aldehydes, amines, and alkenes are possible in these reactions to produce diverse tetrahydroquinoline derivatives in high yield. Moreover, the three-component coupling reactions proceed smoothly in aqueous solution, and commercial formaldehyde-water solution can be used directly (eq 19). Sc(OTf)3-catalyzed three-component aza Diels-Alder cycloadditions also proceed smoothly in an ionic liquid. ... 

An ethanol solution of commercial phenol formaldehyde resin (PFR) was sprayed on a stainless-steel plate [16]. The resin was cross-hnked at 150°C and caibonized at 800°C under N2 environment and further activated at 800°C in CO2 stream. 

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. 

To the remainder of the gelatin solution, add 0 5 to o 8 g. of finely powdered commercial trypsin and incubate at 40 . Carry out the formaldehyde titration on 25 ml. samples at intervals as above. 

Formaldehyde is a gas, b.p. — 21°, and cannot obviously be stored as such moreover, it polymerises readily in the liquid and the gaseous state. The commercial preparation, formalin, is an aqueous solution containing 35-40 per cent, of formaldehyde and some methyl alcohol. The preparation of a solution of formaldehyde may be demonstrated by the following experiment. 

Butynediol. Butynediol, 2-butyne-l,4-diol, [110-65-6] was first synthesized in 1906 by reaction of acetylene bis(magnesium bromide) with paraformaldehyde (43). It is available commercially as a crystalline soHd or a 35% aqueous solution manufactured by ethynylation of formaldehyde. Physical properties are Hsted in Table 2. 

Specifications and Analytical Methods. The commercial aqueous solution is specified as 34% minimum butynediol, as determined by bromination or refractive index. Propargyl alcohol is limited to 0.2% and formaldehyde to 0.7%. 

Viscosities have been measured for representative commercial formaldehyde solutions (21). Over the ranges of 30—50 wt % HCHO, 0—12 wt %... 

Commercial formaldehyde—alcohol solutions ate clear and remain stable above 16—21°C. They are readily obtained by dissolving highly concentrated formaldehyde in the desired alcohol. 

Formaldehyde—Alcohol Solutions. These solutions are blends of concentrated aqueous formaldehyde, the alcohol, and the hemiacetal. Methanol decreases the average molecular weight of formaldehyde oligomers by formation of lower molecular weight hemiacetals. These solutions are used to produce urea and melamine resins the alcohol can act as the resin solvent and as a reactant. The low water content can improve reactivity and reduce waste disposal and losses. Typical specifications for commercially available products are shown in Table 7 (117). 

Biacetyl is produced by the dehydrogenation of 2,3-butanediol with a copper catalyst (290,291). Prior to the availabiUty of 2,3-butanediol, biacetyl was prepared by the nitrosation of methyl ethyl ketone and the hydrolysis of the resultant oxime. Other commercial routes include passing vinylacetylene into a solution of mercuric sulfate in sulfuric acid and decomposing the insoluble product with dilute hydrochloric acid (292), by the reaction of acetal with formaldehyde (293), by the acid-cataly2ed condensation of 1-hydroxyacetone with formaldehyde (294), and by fermentation of lactic acid bacterium (295—297). Acetoin [513-86-0] (3-hydroxy-2-butanone) is also coproduced in lactic acid fermentation. 

Formaldehyde. Pure formaldehyde, CH2O, is a colorless, pungent smelling reactive gas (see Formaldehyde). The commercial product is handled either as soHd polymer, paraformaldehyde (13), or in aqueous or alcohoHc solutions. Marketed under the trade name Formcel, solutions in methanol, / -butanol, and isobutyl alcohol, made by Hoechst-Celanese, are widely used for making alcohol-modified urea and melamine resins for surface coatings and treating textiles. 

Paraformaldehyde [30525-89-4] is a mixture of polyoxymethylene glycols, H0(CH20) H, with n from 8 to as much as 100. It is commercially available as a powder (95%) and as flake (91%). The remainder is a mixture of water and methanol. Paraformaldehyde is an unstable polymer that easily regenerates formaldehyde in solution. Under alkaline conditions, the chains depolymerize from the ends, whereas in acid solution the chains are randomly cleaved (17). Paraformaldehyde is often used when the presence of a large amount of water should be avoided as in the preparation of alkylated amino resins for coatings. Formaldehyde may also exist in the form of the cycHc trimer trioxane [110-88-3]. This is a fairly stable compound that does not easily release formaldehyde, hence it is not used as a source of formaldehyde for making amino resins. 

N,]S7-bis(methoxymethyl)uron was first isolated and described in 1936 (41), but was commercialized only in 1960. It is manufactured (42) by the reaction of 4 mol of formaldehyde with 1 mol of urea at 60°C under highly alkaline conditions to form tetramethylolurea [2787-01-1]. After concentration under reduced pressure to remove water, excess methanol is charged and the reaction continued under acidic conditions at ambient temperatures to close the ring and methylate the hydroxymethyl groups. After filtration to remove the precipitated salts, the methanolic solution is concentrated to recover excess methanol. The product (75—85% pure) is then mixed with a methylated melamine—formaldehyde resin to reduce fabric strength losses in the presence of chlorine, and diluted with water to 50—75% soHds. Uron resins do not find significant use today due to the greater amounts of formaldehyde released from fabric treated with these resins. 

Side-Chain Derivatization. Reaction of thiophene with aqueous formaldehyde solution in concentrated hydrochloric acid gives 2-chloromethylthiophene [765-50-4]. This relatively unstable, lachrymatory material has been used as a commercial source of further derivatives such as 2-thiopheneacetonitrile [20893-30-5] and 2-thiopheneacetic acid [1918-77-0] (24). Similar derivatives can be obtained by peroxide, or light-catalyzed (25) halogenation of methylthiophenes, eg, Ai-bromosuccinimide/benzoylperoxide on 2-, and 3-methylthiophenes gives the corresponding bromomethylthiophenes. 

Liquid Compositions. Urea—formaldehyde reaction products also are available commercially as Hquids that can be categorized into two classes, ie, water suspensions and water solutions. 

Nitrilotriacetonitrile [628-87-5], N(CH2CN)2, a precursor to nitrilotriacetic acid [139-13-9], N(CH2COOH)2, can be prepared from the reaction of formaldehyde cyanohydrin with ammonia (26). Formaldehyde cyanohydrin is also used as an intermediate in pharmaceutical production. Commercial formaldehyde cyanohydrin is available as a 70% aqueous solution stabiLhed by phosphoric acid. 

Commercial aqueous formaldehyde solution, containing about 8% of methanol, was used. 

Commercial aqueous formaldehyde solution containing 8% methanol was used. Formaldehyde is needed in excess otherwise the yield is considerably diminished. 

Formaldehyde is a gas with a boiling point of -21 °C. It is usually supplied as a stabilised aqueous solution ( 40% formaldehyde) known as formalin. When formalin is used as the source of the aldehyde, impurities present generally include water, methanol, formic acid, methylal, methyl formate and carbon dioxide. The first three of these impurities interfere with polymerisation reactions and need to be removed as much as possible. In commercial polymerisation the low polymers trioxane and paraformaldehyde are convenient sources of formaldehyde since they can be obtained in a greater state of purity. 

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