Solutions, formaldehyde Vacuum

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). 

Mix 50 ml. of formalin, containing about 37 per cent, of formaldehyde, with 40 ml. of concentrated ammonia solution (sp. gr. 0- 88) in a 200 ml. round-bottomed flask. Insert a two-holed cork or rubber stopper carrying a capillary tube drawn out at the lower end (as for vacuum distillation) and reaching almost to the bottom of the flask, and also a short outlet tube connected through a filter flask to a water pump. Evaporate the contents of the flask as far as possible on a water bath under reduced pressure. Add a further 40 ml. of concentrated ammonia solution and repeat the evaporation. Attach a reflux condenser to the flask, add sufficient absolute ethyl alcohol (about 100 ml.) in small portions to dissolve most of the residue, heat under reflux for a few minutes and filter the hot alcoholic extract, preferably through a hot water fuimel (all flames in the vicinity must be extinguished). When cold, filter the hexamine, wash it with a little absolute alcohol, and dry in the air. The yield is 10 g. Treat the filtrate with an equal volume of dry ether and cool in ice. A fiulher 2 g. of hexamine is obtained. 

Resoles. Like the novolak processes, a typical resole process consists of reaction, dehydration, and finishing. Phenol and formaldehyde solution are added all at once to the reactor at a molar ratio of formaldehyde to phenol of 1.2—3.0 1. Catalyst is added and the pH is checked and adjusted if necessary. The catalyst concentration can range from 1—5% for NaOH, 3—6% for Ba(OH)2, and 6—12% for hexa. A reaction temperature of 80—95°C is used with vacuum-reflux control. The high concentration of water and lower enthalpy compared to novolaks allows better exotherm control. In the reaction phase, the temperature is held at 80—90°C and vacuum-refluxing lasts from 1—3 h as determined in the development phase. SoHd resins and certain hquid resins are dehydrated as quickly as possible to prevent overreacting or gelation. The end point is found by manual determination of a specific hot-plate gel time, which decreases as the polymerization advances. Automation includes on-line viscosity measurement, gc, and gpc. 

Meerwein s Ester (9) Dimethyl malonate (13.2 g, 0.4 mole) and 6 g of 40 % aqueous formaldehyde solution are mixed in an Erlenmeyer flask and cooled to 0° in an ice bath. To the mixture is added 0.3 g of piperidine and enough ethanol to produce a homogeneous solution. The solution is allowed to stand at 0° for 12 hours, at room temperature for 24 hours, and at 35 0° for 48 hours. The reaction product is washed with water (50 ml) followed by dilute sulfuric acid, then dried (sodium sulfate). Unreacted malonic ester is distilled off under vacuum leaving a residue of about 12.5 g, which contains methylenemalonic ester, methylenebismalonic ester, and hexacarbomethoxypentane. 

To 217 grams (0.456 mol) of N,N -bis[1-methyl-3-(2,2,6-trimethylcyclohexyl)propyll-I.B-hexanediamine were added 182 ml (3.04 mols) of formic acid (90%). The resulting colorless solution was cooled, then 91.3 ml (1.043 mols) of formaldehyde (37%) were added. The solution was heated at steam temperature with occasional shaking for 2 hours and then refluxed for 8 hours. The volatiles were distilled off at steam temperature under water vacuum and the residual oil was made strongly alkaline with 50% potassium hydroxide. 

A further quantity of arabinose may be isolated from the mother liquors by the use of diphenylhydrazine to a solution of 22 g. of diphenylhydrazine hydrochloride in 100 cc. of absolute methyl alcohol is added a solution of 3.3 g. of sodium in 50 cc. of methyl alcohol. After fifteen minutes standing the sodium chloride is removed by filtration and washed with methyl alcohol. The filtrate, which contains approximately 18 g. of free diphenylhydrazine, is added to the alcoholic mother liquor from the arabinose and the mixture is inoculated with diphenylhydrazone prepared from some of the crystalline arabinose. The mixture is allowed to stand overnight, and the crystalline diphenylhydrazone is filtered, washed with 95 per cent ethyl alcohol, and dried in a vacuum desiccator. In a preparation in which the yield of crystalline arabinose had been 23.5 g., the yield of diphenylhydrazone was 16.5 g., corresponding to 7.8 g. of the sugar. Arabinose can be recovered from the diphenylhydrazone by treatment with formaldehyde in aqueous solution. In view of the... 

Tellurophene. A mixture of tellurium (4.0 g, 31 mmol), sodium formaldehyde sulphoxylate of 85% (28 g, 200 mmol), sodium hydroxide (17 g, 425 mmol) in 150 mL water is heated at reflux, under N2 atmosphere for 15 min, and then cooled at 20°C. A solution of 1,4-bis(trimethylsilyl)-l,3-butadiene (8.2 g, 42 mmol) in 100 mL of ethanol is slowly added to the stirred sodium telluride solution, the mixture is heated at reflux for 15 min, then stirred at 20°C for 3 h and extracted with ether. The extract is dried (Na2S04), filtered, and 10 mL (200 mmol) of bromine are added dropwise until the bromine colour persists. This solution is concentrated in a water bath under aspiration vacuum to a volume of 50 mL, and the red precipitate of tellurophene dibromide is collected 8.9 g (84%), m.p. 120°C dec. 

Methylamine Hydrochloride. 125 g of ammonium chloride and 250 g 40% aqueous formaldehyde solution are placed in a distilling apparatus, with the thermometer well below the surface of the liquid. The mixture is slowly heated to 104° and held at this temp until no more liquid distills. The product in the flask is cooled and filtered from ammonium chloride. The liquid is then evaporated on a water bath to half its original volume and a second crop of ammonium chloride is filtered off. The filtrate is concentrated at 10(T until a crystalline scum forms on the surface. On cooling methylamine hydrochloride separates and is removed by filtration. Further evaporation and cooling produces another crop of methylamine hydrochloride, which is also filtered. The combined yield is treated with boiling chloroform, filtering hot, washed with room temp chloroform, and dried in a vacuum desiccator. Yield 40 g. 

Dimethylolnitramine (252) readily participates in Mannich condensation reactions treatment of a aqueous solution of (252) with methylamine, ethylenediamine and Knudsen s base (254) (generated from fresh solutions of ammonia and formaldehyde) yields (253), (255) and (239) (DPT) respectively. The cyclic ether (258) is formed from the careful dehydration of dimethylolnitramine (252) under vacuum. ... 

Urea-formaldehyde resins are generally prepared by condensation in aqueous basic medium. Depending on the intended application, a 50-100% excess of formaldehyde is used. All bases are suitable as catalysts provided they are partially soluble in water. The most commonly used catalysts are the alkali hydroxides. The pH value of the alkaline solution should not exceed 8-9, on account of the possible Cannizzaro reaction of formaldehyde. Since the alkalinity of the solution drops in the course of the reaction, it is necessary either to use a buffer solution or to keep the pH constant by repeated additions of aqueous alkali hydroxide. Under these conditions the reaction time is about 10-20 min at 50-60 C. The course of the condensation can be monitored by titration of the unused formaldehyde with sodium hydrogen sulfite or hydroxylamine hydrochloride. These determinations must, however, be carried out quickly and at as low temperature as possible (10-15 °C), otherwise elimination of formaldehyde from the hydroxymethyl compounds already formed can falsify the analysis. The isolation of the soluble condensation products is not possible without special precautions, on account of the facile back-reaction it can be done by pumping off the water in vacuum below 60 °C imder weakly alkaline conditions, or better by careful freeze-drying. However, the further condensation to crosslinked products is nearly always performed with the original aqueous solution. 

On a commercial scale, hexamine is manufactured from anhydrous NHi and a 45% solution of methanol-free formaldehyde. These raw materials, plus recycle mother liquor, arc charged continuously ai carefully controlled rates 10 a high-velocity reactor. Tile reaction is exothermic. "Die reactor effluent is discharged into a vacuum evaporator which also serves as a... 

SYNTHESIS To a solution of 72.3 g 2,6-dimethoxyphenol in 400 mL MeOH, there was added 53.3 g of a 40% solution of aqueous dimethylamine folowed by 40 g of a 40% aqueous solution of formaldehyde. The dark solution was heated under reflux for 1.5 h on a steambath. The volatiles were then removed under vacuum... 

Adding aqueous formaldehyde solution to a reaction kettle can also make Hexamine. Then ammonia gas (in a 3 2 formaldehyde/ammonia mole ratio) is added. During the addition of the reactants, the temperature is maintained at about 20 to 30°C. The reaction mixture is then fed to a vacuum evaporator where it is maintained at a temperature between 30 and 50X1 and at a pH of 7 to 8252. 

The ammonia-formaldehyde reaction is highly exothermic. Therefore the reactor is operated under a vacuum so that the heat of reaction can be used to evaporate some of the water of reaction. This helps concentrate and crystallize the hexamine in the water solution. If dry solids are desired, the hexamine-water solution is pumped through a crystals receiver and then separated in a centrifuge. The crystals pass through a rotary dryer and are packaged for shipment. In some cases a liquid solution may be shipped to customers125. 

RNAs are denatured by formaldehyde/heat treatment. All of the stock solutions for RNA slot blots are made using sterile diethyl pyrocarbonate (DEPC)-treated water. RNAs are diluted as necessary from stock solutions with water, and 3 volumes of 6.15 Mformaldehyde in 10X standard saline citrate (SSC) is added to give a final RNA concentration of 10-100pg/ml. The RNA dilutions are heated to 65° for 15 min and quick-chilled on ice. The denatured stock is further diluted with 4.16 M formaldehyde in 7.5 X SSC such that the desired concentration of RNA may be applied to each slot in a total volume of 400 pi. The nylon membrane is piewet in water and then soaked in 10X SSC for 20 min. Slot blots are performed using a commercially available apparatus hooked to a vacuum source. After the samples are blotted through, each well is washed with 400 pi of 10 X SSC. The membrane is removed from the apparatus and baked in a vacuum oven at 80° for 2 hr. 

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