United States Patent Office 2,807,613 Patented Sept. 24, 1957 s s 2 2,807,613 nol, where it may exist in the form of a hemiformal, or PREPARATION OF 6-METHYL-6-PHENYLTETRA of a revertible polymer. Usually formaldehyde is used in HYDRO-1,3-OXAZINES excess based on molar proportions referred to the a Claude 5. Schmide, Moorestown, and Richard C. Maas 5 methylstyrene, proportions from about 1.5:1 to 5:1 being field, Haddon afield, N. J., assignors to Rohm & Hiaas practical. Of course, with less than a 2:1 proportion Company, Philadelphia, Pa., a corporatica of Delaware unreacted starting materials may be present in the react ing mixture, Preferred proportions are from 2:1 to 4:1. No Drawing. Application April 3, 1955, Ammonia may be supplied as a gas or as an aqueous Serial No. 577,944 solution or in the form of ammonium chloride or bromide. 7 Claims. (C. 260-244) 0 Of course, if ammonia or ammonium hydroxide is used, This invention deals with a method for improving yields it will react with the hydrochloric or hydrobromic acid of 6-methyl-6-phenyltetrahydro-1,3-oxazines when made which is added as catalyst. The same final result is ob from an O-methylstyrene, formaldehyde, and ammonia. tained by use of the preformed ammonium halide, which In United States Patent 2,647,117, there is described 5 Supplies both the ammonia and the catalyst. The amount the reaction of olefins, including c-methylstyrene, with of ammonia or ammonium compound is usually at least ammonia and formaldehyde in the presence of hydrogen equivalent to the c-methylstyrene and may be in consid -chloride as a catalyst. The reaction yields a mixture of erable excess thereof. The preferred ratios of ammonia various products from which there can be separated by to an cy-methylstyrene are from about 1.5:1 to 2.5:1. distillation a modest yield of 6-methyl-6-phenyltetrahy 20 The order in which the c-methylstyrene, formalde dro-1,3-oxazine as an especially useful material. hyde, ammonia, and catalyst are mixed is immaterial. A Way has now been found to increase the yield of this Formaldehyde and ammonia or ammonium halide may be compound and other 6-methyl-6-phenyltetrahydro-1,3- mixed, even though there may be interaction and an ox oxazines as prepared by the reaction of an a-methylsty methylstyrene added to this mixture or the mixture to the rene, formaldehyde, and ammonia in the presence of a a-methylstyrene. Other orders of mixing are likewise ef hydrogen halide. After these materials have been brought fective. together and preferably reacted, there is added to the re If an ammonium halide is not used, hydrochloric acid action mixture methanol and the resulting mixture is or hydrobromic acid or hydrogen chloride or hydrogen heated and distillate taken therefrom until methanol and bromide is added at any convenient stage. The amount other materials distilling therewith, such as methylal, have 30 supplied is usually best about equivalent to the ammonia, been substantially removed. The reaction mixture is then but smaller or larger amounts may be used. The cata rendered alkaline by addition of water-soluble basic ma lysts have a molecular weight from about 36 to 81. terial, such as sodium or potassium hydroxide or car The reaction nixture is heated between about 45 and bonate or ammonium hydroxide. The desired 6-methyl about 120° C. until good conversion is obtained. The 6-phenyltetrahydro-1,3-oxazine, separates as an oil, is reaction is exothermic, and sometimes it may be desirable taken off, and purified as by distilling. The yield is now to limit the rate of addition of reactants and/or supply double that obtained by immediate separation of an oil cooling. Usually in one-half to four hours reaction is from the reaction mixture and its distillation as heretofore complete. The reaction mixture may, if desired, be heat practiced. During the methanol treatment it is evident ed for a longer time, particularly when larger ring-substit some substance or substances are converted to the desired 40 uents are present. - -- tetrahydrooxazine. There is then added about one to twelve moles of As an O-methylstyrene there may be used c-methylsty methanol per mole of the a-methylstyrene and the result rene itself or a ring substituted cy-methylstyrene with elec ing mixture is best warmed to initiate reaction. The mix tron-doning groups, as in an cz-methylstyrene in which ture is then heated to reflux, then distilled, and distillate the ring substituent is one such as an alkyl group, particu 45 is taken off until substantially all or most of the methanol larly an alkyl group of not over four carbon atoms, an present and other materials distilling therewith such as ether group such as the methoxy or ethoxy group or an methylal are removed. The residue is rendered alkaline. aryl group or a cycloalkyl group. Typical starting mate The oil which forms is separated and distilled under re rials are p,c-dimethylstyrene, m,0-dimethylstyrene, op duced pressure. - - - at-trimethylstyrene, o, o' - oz - trimethylstyrene, . p-ethyl-a- 50 The 6-methyl-6-phenyltetrahydro-1,3-oxazines, which methylstyrene, m-ethyl-O-methylstyrene, p-isopropyl-or are thus obtained are useful as corrosion inhibitors, as methylstyrene, p-tert-butyl-o-methylstyrene, p-cyclohexyl catalysts for use as a weak base for preparing poly c-methylstyrene, p-phenyl-o-methylstyrene, p-methoxy-a- urethane foams, and as chemical intermediates, being re methylstyrene, p-ethoxy-o-methylstyrene, c- or g-isopro arranged by strong acids to tetrahydropyridines from which piperidinois and their esters can be prepared. penylnaphthalene, or isopropenylmethylnaphthalene. The . A good procedure for preparing 6-reihyl-6-phenyltetra preferred starting compounds may be defined by the gen hydro-1,3-oxazines is given in the following detailed ex eral formula ample, which is given by way of illustration and not by CHs way of limitation, the procedure being generally applica 30 ble to the reaction of any of the above incited cy-methyl (-on, styrenes, their homologues or isomers. There are mixed 236 parts by weight of a-methyl styrene, 668 parts of aqueous 37% formaldehyde solu 65 tion, and 216 parts of ammonium chloride. The mixture is stirred and heated to about 60° C. An exothermic where R is hydrogen, alkyl of not over four carbon atoms, reaction ensues which is controlled by external cooling cycloalkyl, phenyl, or alkoxy cf not over two carbon to maintain the temperature at about 55-65 C. When atoms. Other hydrogen-doning groups are equivalent to the exothermic reaction is over, the reaction mixture is these. 70 allowed to cool to about 40° C. over a period of about Formaldehyde may be used in the form of aqueous so an hour. There is added methanol to a total of 450 parts. lutions, of solutions in alcohols, 'conveniently in metha The mixture is stirred for several hours and later heated rt - 2,807,618 . -- " " - 3 4 - on a steam bath. Distillate is taken off. The alcohol-free wherein R is a member of the class consisting of hydro mixture at this point contains the hydrochloride salt of gen, alkyl groups of not over four carbon atoms, cyclo 6-methyl-6-phenyltetrahydro-1,3-oxazine. If desired, this alkyl groups, the phenyl group, and alkoxy groups of not salt could be isolated, or utilized directly as it exists in over two carbon atoms, formaldehyde, and ammonia, the solution, for many purposes, e. g. as a corrosion inhibitor formaldehyde and ammonia being in molecular excess of or as a chemical intermediate for forming many other the said c-methylstyrene, in the presence of a hydrogen useful products. If it is desired, however, to isolate the halide of a molecular weight from about 36 to 81 in an free base, the alcohol-free mixture is treated with aqueous amount about equivalent to the ammonia, adding metha 50% sodium hydroxide solution until basic. An oil sep nol to the reaction product and heating this mixture to arates and is taken up with toluene, the organic layer 10 reflux, distilling the mixture, removing the distillate until being separated, dried, and distilled. At 95-1 i0° C./A most of the methanol present and other products, such mm. there are obtained 236 parts of 6-methyl-6-phenyl as methylal, distilling therewith have been removed, add tetrahydro-1,3-oxazine. This is redistilled and a center ing a water-soluble basic material, whereby an oil is cut taken for analysis. It has a refractive index, n.5, formed, and separating out the oil which is the desired of 1.5382 and contains by analysis 74.58% of carbon, 6-methyl-6-phenyltetrahydro-1,3-oxazine. - 8.94% of hydrogen, and 7.74% of nitrogen, theory being 3. A process for preparing 6-methyl-6-phenyltetrahy 74.54%, 8.53%, and 7.90% respectively. The yield is dro-1,3-oxazine which comprises reacting between about 67%. 45 and 125 C. a-methylstyrene formaldehyde, and The hydrochloride is formed therefrom upon addition ammonia in the presence of hydrogen chloride, the form of an equivalent amount of hydrochloric acid. This salt 20 aldehyde and ammonia being in molecular excess of the is recrystallized from acetone containing 5% isopropyl c-methylstyrene and the hydrogen chloride being about alcohol. The hydrochloride melts at 147-149 C. By equivalent to the ammonia, adding methanol to the re analysis it contains 61.15% of carbon, 7.67% of hydro action product and heating this mixture to reflux, distilling gen, 6.62% of nitrogen, and 16.7% of chlorine.