PROCESS FOR PREPARING TRICHLOROMELAMINE

Abstract: A process for preparing trichloromelamine starting from chlorine and melamine with intermediate formation of an aqueous suspension of hexachloromelamine, characterized in that hexachloromelamine is solubilized by addition of a water-immiscible solvent, the aqueous phase is separated and the hexachloromelamine solution is brought into contact, in the presence of an activator, with a number of moles of mela­ mine which is equal to or lower than the number of moles of the yet present hexachloromelamine.

Description: The processes for preparing chloromelamines disclosed in the literature (see US-A-2 472 361, GB-A-931 747 and SU-­ A-143 382) involve reactions in aqueous phase between melamine and chlorine or melamines and hexachloromelamine. A major drawback resides in the difficulty experienced in drying the resulting product which, even after centrifugation, retains considerable amounts of water which results in the formation of crumbs which are difficult to pulverize. Another serious drawback is the chemical aggressivity of the reaction medium (presence of HCl and HClO), which makes it necessary to use expensive, highly corrosion-resistant materials, not only in the reaction section but also in the subsequent sections of the plant (filtering and drying). The applicant has now developed a very simple and practical method which fully eliminates the above-mentioned drawbacks. In its most general form the invention relates to a process for preparing trichloromelamine starting from chlorine and melamine, with intermediate formation of an aqueous suspen­ sion of solid hexachloromelamine, characterized in that the hexachloromelamine so formed is solubilized by addition of a water-immiscible solvent, the aqueous phase is separated and the resulting substantially anhydrous hexachloromelamine solution is contacted, in the presence of an activator, with a number of moles of non-chlorinated melamine either equal to or lower than the number of moles of hexachloromelamine yet present. The trichloromelamine according to the present invention is 2,4,6-trichloroamino-1,3,5-triazine of formula (I): Several embodiments of the invention are possible. According to a particularly advantageous embodiment, gaseous chlorine is bubbled into an aqueous suspension of melamine under stirring, the feeding rate of chlorine being adjusted in such a way, that the whole chlorine amount be absorbed. The water/melamine weight ratio can range from 20 to 100 (prefer­ ably it is about 50) and the reaction time is generally a few tens of minutes at room temperature. The reaction can take place also by substituting a mixture containing an alka­ line hypochlorite and an acid, either organic or inorganic, for chlorine. A hexachloromelamine suspension is thus obtained, to which, always under stirring, an amount of a solvent (for ex­ ample carbon tetrachloride) capable of dissolving all the hexa­ chloromelamine is added. The aqueous phase is separated, which, if so desired, can be utilized again in the first reaction step-­ after removal of the hydrochloric acid - by means of neutrali­ zation, or treatment with ion-echange resins or another equiva­ lent technique. Such re-utilization permits to recover the me­ lamine fraction which has remained in solution in the aqueous phase at concentrations equal to about 0.3% by weight. Subse­ quently, and always under stirring, melamine, in an equimolar amount or slightly in defect with respect to hexachloromelamine, is added to the hexachloromelamine solution. An activator (or promoter), for example H₂O and/or acetic acid or other inorganic or organic acids, is then added, and the whole is kept under stirring, at the solvent reflux temperature, for the time re­ quired to convert hexachloromelamine (generally 1 to 6 hours). Residual hexachloromelamine was removed by filtration and washing with the solvent. The filtration and washing liquids can be re-­ used to solubilize the hexachloromelamine in a subsequent pro­ cessing. The solid product, after evaporation of the residual solvent, appears as a very fine white powder. The melamine conversion is usually about 90% but can also reach higher values if longer reaction times are employed. The following examples are given to illustrate the invention more in detail, but they are not to be construed as a limitation of the scope of the invention. EXAMPLE 1 Into a suspension of 21 g of melamine in 1 000 g of water, maintained under intense stirring at room temperature, there was bubbled a chlorine flow, taking care that all the chlorine should be absorbed. After 30 minutes at 20°C, a hexa­ chloromelamine suspension with a percentage of available chlor­ ine equal to 127% was obtained. "Available chlorine" means twice the percentage-by-weight of the chlorine contained in the chlorinated melamine. Always under stirring, 1400 g of carbon tetrachloride were added to this suspension in order to dissolve all the hexachloromelamine. Stirring was stopped, to permit the separation of the organic phase from the aqueous phase and, after removal of the latter, 14.8 g of melamine were added under stirring. The resulting suspension was brought to reflux temperature (77°C) and after addition, by means of a proper sparger, of 4 g of water, it was refluxed during 6 hours. The product was filter­ ed, washed with CCl₄ and dried in an oven at 80°C. Obtained were 43.1 g of trichloromelamine with an active chlorine content of 86.5% (corresponding to a yield of 80%). EXAMPLE 2 Example 1 was repeated until separation of the solution of hexachloromelamine in carbon tetrachloride. The solution was then concentrated by distillation of a portion of the sol­ vent in order to obtain a 15% by weight of dissolved hexachloro­ melamine. 14.8 g of melamine, 1.2 g of acetic acid and 1.2 g of water were added to such solution, maintained at reflux tem­ perature under intense stirring, whereupon it was allowed to react for 6 hours at boiling temperature. The reaction product, after filtration, washing with CCl₄ and drying in an oven at 80°C, appeared as a very fine white powder and consisted of trichloromelamine with 90% of available chlorine (corresponding to a yield of 90%).

Claims: 1. A process for preparing trichloromelamine starting from chlorine and melamine with intermediate formation of an aqueous suspension of solid hexachloromelamine, charac­ terized in that the thus formed hexachloromelamine is solubilized by addition of a water-immiscible solvent, the aqueous phase is separated and the resulting substan­ tially anhydrous solution of hexachloromelamine is brought into contact, in the presence of an activator, with a number of moles of non-chlorinated melamine equal to or lower than the number of moles of present hexachloromelamine. 2. The process according to claim 1, wherein said solvent is carbon tetrachloride, in amounts preferably ranging from 3 to 35 kg for each kg of hexachloromelamine. 3. The process according to claim 1 or 2, wherein the hexa­ chloromelamine solution is concentrated, by distillation of a part of the solvent, before being brought into contact with the non-chlorinated melamine. 4. The process according to any one of claims 1 to 3, wherein the residual solvent, after filtration and washing of trichloromelamine, is re-used for solubilizing hexachloro­ melamine. 5. The process according to any one of claims 1 to 4, wherein the activator is selected from water, acids and mixtures thereof. 6. The process according to claim 5, wherein the activator is a mixture of water and acetic acid in a molar ratio preferably of from 1 to 10.

Inventors: BUSATI, VAIFRO, CORSO, GIAMPIETRO, DALL'ACQUA, DINO, TALAMINI, GIANPIETRO
Applicants: MONTEDIPE S.R.L.
Application year: 1987
Main classification: C07D251
IPC codes: C07D251