Patent GB-1028804-A (GB)
Title: Paraformaldehyde
Filed: 1963-07-16
Abstract: The invention comprises stabilized paraformaldehyde having a formaldehyde content higher than 80%, a water solubility at 50 DEG C. of about 95% in 30-40 mins., an average degree of polymerization between 15 and 70 corresponding to an average molecular weight between 450 and 2100 and containing from 0.01 to 5% by weight of a triazine stabilizer having the general formula  <FORM:1028804/C2/1> in which R1 is a hydrogen atom or an alkyl, aryl, a partially or completely hydrogenated aryl, aryl ortho-substituted with a guanamine radical or alkylaryl group, or an alkylamino or amino alkenyl group which may be substituted by hydrocarbon groups, and R2 and R3 are the same or different and are hydroxyl or aryl groups which may be hydrogenated or substituted in the benzene ring, or amine groups -NR1R11 in which R1 and R11 are hydrogen atoms or aryl, alkyl or alkenyl groups which may be substituted with hydroxy groups.  Solid crystalline paraformaldehyde having a formaldehyde content higher than 96% may be obtained by drying the stabilized paraformaldehyde. Concentrated aqueous formaldehyde solutions having a formaldehyde content of 36-45% by weight, may be obtained by dissolving the stabilized paraformaldehyde in water.  The stabilized paraformaldehyde may be obtained by the concentration and cooling of an alkaline formaldehyde solution containing the stabilizer and centrifuging the slurry obtained. The stabilized paraformaldehyde may be obtained in the form of flakes by concentrating the stabilized alkaline formaldehyde solutions to a formaldehyde concentration of at least 80% (by weight) adjusting the pH to 8-10 at a temperature of 80-100 DEG  C., quenching on a metal surface and then scraping off the solid paraformaldehyde in the form of flakes. Suitable stabilizers of the above general formula are, for example, benzoguanamine, diallyl melamine and tetrahydrobenzoguanamine.  It appears that the stabilizer reacts with the formaldehyde to form methylol groups but the mechanism of the stabilization is not known.ALSO:Stabilized paraformaldehyde having a formaldehyde content higher than 80%, a water-solubility at 50 DEG  C. of about 95% in 30-40 mins., an average degree of polymerization between 15 and 70 corresponding to an average molecular weight between 450 and 2100 contains from 0.01-5% by weight of a triazine stabilizer having the general formula <FORM:1028804/C3/1> in which R1 is a hydrogen atom or an alkyl, aryl, a partially or completely hydrogenated aryl, aryl ortho-substituted with a guanamine radical or alkylaryl group or an alkylamino or aminoalkenyl group which may be substituted by hydrocarbon groups, and R2 and R3 are the same or different and are hydroxyl or aryl groups which may be hydrogenated or substituted in the benzene ring, or amine groups -NR1R11 in which R1 and R11 are hydrogen atoms or aryl, alkyl or alkenyl groups which may be substituted by hydroxy groups.  Solid crystalline paraformaldehyde having a formaldehyde content higher than 96% may be obtained by drying the stabilized paraformaldehyde.  The stabilized paraformaldehyde may be obtained by the concentration and cooling of an alkaline formaldehyde solution containing the stabilizer and centrifuging the slurry obtained.  The stabilized paraformaldehyde may be obtained in the form of flakes by concentrating the stabilized alkaline formaldehyde solution to a formaldehyde content of at least 80% (by weight) adjusting the pH to 8-10 at a temperature of 80-100 DEG  C., quenching on a metal surface and scraping off the solid paraformaldehyde in the form of flakes.  Suitable stabilizers of the above general formula are, for example, benzoguanamine, diallylmelamine and tetrahydrobenzoguanamine.