Distillation, formaldehyde solutions Vacuum

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. 

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. 

Inoidazole (20.4 g, 0.3 mol) and 97% dimethylamine hydrochloride (26.0 g, 0.3 mol) are dissolved in water (50 ml), and concentrated hydrochloric acid is added until the pH is below 5. Aqueous formaldehyde solution (37%, 27 g, 0.33 mol) is added, and the mixture is allowed to stand at room temperature (48 h). The solution is made strongly alkaline with 20% potassium hydroxide solution, and the organic material is salted out with potassium carbonate, and extracted with chloroform. The combined organic layers are dried (K2CO3) and concentrated to give an oil, which is distilled under vacuum to give the pure product (29 g, 78%), b2 100-102 C, bi.5 95°C. 

Other polycondensation reactions which lead to finely dispersed polymers in liquid polyethers are the polycondensation reactions of urea and melamine with aqueous formaldehyde [92-95]. The reaction medium is usually polyether polyols, PO homopolymers or PO-EO copolymers (random or block copolymers), with MW of 3000-5000 daltons. During the polycondensation reaction, the aminoplast polymer precipitates, being insoluble in polyether and water (water from formaldehyde solution and reaction water), is eliminated by vacuum distillation. A variant of this reaction is to develop the polycondensation in water, and water containing the aminoplast polymer (as a viscous solution) is added to a polyether polyol, under vacuum, and at high temperature (100-130 °C), water being continuously eliminated from the reaction medium. The aminoplast insoluble polymer precipitates in the form of fine particles. 

An introduction to the typical resin synthesis of a UF resin used as an adhesive for wood products and in industrial applications is given below. It constitutes a handy formulation for those who want to work in this field. It is not a low-formaldehyde-emission formulation. To 1000 parts by mass of 42% formaldehyde solution (methanol < 1%) are added 22% NaOH solution to pH 8.3 to 8.5,497 parts by mass of 99% urea, and the temperature raised in 50 min from ambient to 90°C while maintaining pH in the range 7.3 to 7.6 by small additions of 22% NaOH. The temperature is maintained at 90 to 91°C until the turbidity point is reached (generally another 15 to 20 min). The pH is then corrected to 4.8 to 5.1 by addition of 30% formic acid, and the temperature is raised to 98°C. The water tolerance point is reached in 18 min and the pH is then adjusted to 8.7. Vacuum distillation of the reaction water with concomitant cooling is then initiated. After distillation of the wanted amount of water to reach a resin content of 60 to 65%, the resin is cooled to 40°C, 169 parts by mass of second urea is added, the pH is adjusted to 8.5 to 8.7, and the resin is allowed to mature at 30°C for 24 to 48 h resin characteristics solids content, 60% density, 1.268 g/cm free HCHO, 0.4% viscosity, 200cP pH, 8. 

Vacuum Distillation. jSince the pai-tial pressiue of formaldehyde over its aqueous solutions is extremely low at ordinaiy temperatures, vacuum distillation affords a method for concentratiug foi maldehj de. This fact as first ob. en ed by Butlerov in 1859. During vacuum distillation, formaldehyde hA drates concentrate in the stih with erentmal fonnation of the soUd mixtme of polymeric hydi-ates knorra as paraformaldehyde. Thi. procedure has long been used commercially for the preparation of p3rai omla deh de and. special process modifications have been described in patents ... 

Formaldehyde solutions may be readily concentrated by vacuum distillation, and this procedure has long been used commercially for the production of parafoimaldehyde . Dilute foimaldebyde. solution is distilled and paraformaldehj de is left behind as a still residue. 

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. 

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). 

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. 

In the case of phenol, with the free para position, due to the interaction between the phenolic group (acidic) and the aminic nitrogen (basic) of the amino alcohol, the ortho position is occupied first [9]. After the synthesis of Mannich bases, the water resulting from the reaction and the water from the aqueous solution of formaldehyde is distilled under vacuum, at 90-125 °C (preferably in the range 90-100 °C). A low range of distillation temperatures is preferred in order to avoid the tendency of the Mannich base to condensate to superior oligomers (with 2-3 aromatic nuclei), which increase substantially the viscosity of Mannich base and, of course, of final Mannich polyol. The mechanism of the Mannich reaction is considered to be a two-step mechanism. In the first step the reaction between formaldehyde and the primary or secondary amine (reaction 15.2) takes place, with the formation of an immonium cation [7-9, 22, 23]. 

Selective reaction of cardol in preference to cardanol under Mannich reaction conditions with diethylenetriamine (or 4-aminobutane) and aqueous formaldehyde in methanolic solution resulted in the separation, as a lower layer, of the cardol in the form of a low polymeric Mannich base. Recovery of cardanol from the upper layer and high vacuum distillation afforded pure material containing only traces of 2-methylcardol (ref. 189). Thus technical CNSL (1 mole average mol. wt. 303g) with 40% aqueous formaldehyde (1.2 mole CHjO) and diethylenetriamine (0.125 mole) in methanol (1250ml) afforded after 30mins a dark methanol-insoluble lower... 

Monomeric partially and fully alkylated amino resins are prepared in two separate reaction steps. Hydroxymethylation is carried out under basic conditions to minimize self-condensation of the amino resin. The pH is then lowered by addition of a mineral acid and alkylation with methanol is carried out. To obtain monomeric amino resins, an excess of formaldehyde has to be used to assure a high level of hydroxymethylation and a low level of residual amide groups that would otherwise lead to polymer formation during the alkylation step. Since water removal by azeotropic distillation is not possible with methanol, a large excess of alcohol is required to achieve complete alkylation. After completion of alkylation the resin solution is neutralized water, alcohol, and residual formaldehyde are removed by vacuum distillation. The salt formed during neutralization is removed by filtration [2.154]. 

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