Oct. 19, 1943. E. : C, SOULE 2,332,179 METHOD OF PRODUCING PHENAZINE OXIDE Filed Oct. 1, 1940 2 Sheets-Sheet li Coozz? AORNEYs Patented Oct. 19, 1943 2,332,179. UNITED STATES PAT ENT OFFCE 2,332,179. METHOD OF PRODUCING PHENAZINE oXIDE . Edward Cornelius Soule, Niagara Falls, N.Y., as signor to The Mathieson Alkali Works, Ing., New York, N.Y., a corporation of Virginia. Application October 1, 1940, Seria. No. 359,234. 15 Claims. (CI. 260-267) This invention relates to improvements in the attempting to carry out this process on a large production of phenazine oxide (di-benzo-para Scale... there is danger of explosion if the Vapors di-azine oxide), and -phenazine therefrom, from are confined. nitrobenzene and aniline by an alkaline conden I have found, however, that the condensation sation reaction. of aniline with nitrobenzene in the presence of The present. invention provides an improved finely, ground potassium hydroxide: can be car process for the production of phenazine oxide ried out · Smoothly and without objectionable from aniline and nitrobenzene in which the alka autocatalytic action if the condensation is con line condensation reaction is carried out in the ducted in the presence of an inert diluting sol presence of an inert diluting SOVent. With result 0 vent. Such as benzene, toluene, hexane, ligroin, ing advantages in temperature control, increased etc. which will be appreciably miscible with both yields of phenazine oxide based on the aniline nitrobenzene and aniline. In the presence of a used and reduction or elimination of the forma diluting inert solvent the temperature of con tion of undesirable by-products. ihe invention densation may be advantageously held between provides an improved process in which an excess 15 such temperature limits as 60° C. to 130° C. for of nitrobenzene is advantageously employed with a sufficient length of time to insure substantially resulting increase, in yield of phenazine oxide complete usage of all of the aniline charged, and and reduction in amount of azobenzene formed. particularly so where a sufficient amount of nitro The invention also provides an improved process benzene is used. Between these temperature which is advantageously carried out in a cyclic 20 limits the condensation will proceed to Substan manner with reuse of the solvent, and of the ex tial completion with a minimum of by-products cess nitrobenzene and also With reuse of the alka and a maximum of safety of operation. The line cake produced as a by-product of the reac inert diluting solvents are advantageously so tion in the further carrying out of the reaction. chosen, or mixtures thereof so chosen, as to regu The invention also includes improvements in the 25 late the temperature of the reaction by the re separation and purification of the phenazine ox fluxing of the solvent. ide. The invention includes various features and I have also found that substantial improve improvements, which, or certain of which, are ments in yield and purity of phenazine oxide, capable of conjoint use in carrying out the proc and of phenazine therefrom, and reduction of ess and are advantageously used in doing. So. 30 undesirable by-products, can be effected by main The nature and advantages of the invention and taining the nitrobenzene in molecular excess over of its various improvements will be more fully the aniline charged for condensation. By em described in the following. more detailed descrip ploying a sufficient excess of nitrobenzene over tion. - aniline in the condensation charge, the mech It has heretofore been proposed to carry Out 3 5 anisms of the condensation may be so changed as the condensation of nitrobenzene and aniline, to favor the formation of phenazine oxide, while used in equal proportions by weight, in the pres substantially eliminating undesirable by-products ence of caustic potash, but the chief product ob such as tar, carbon and ammonia. In addition, tained is azobenzene, with a relatively low yield the yields of undesirable azobenzene can be mate of phenazine oxide, and with the production of rially decreased as the mole excess of nitro undesirable by-products. In attempting to carry benzene over aniline is increased until at large out this process by condensing aniline, a reduc excesses the azobenzene is almost completely ing agent, with nitrobenzene, an oxidizing agent, eliminated, and a high yield of phenazine oxide, in the presence of finely ground caustic potash, based on the aniline, is obtained. I have found that this operation is a dangerous The process is particularly advantageous when one and difficult to control. As the temperature both an inert solvent and an excess of nitro is carefully raised to cause the condensation to benzene are employed. Since it is primarily the begin, reaction occurs autocatalytically with such reaction of finely ground solid caustic potash on suddenness and vigorous evolution of heat as to nitrobenzene which is responsible for the auto cause a temperature rise in an uncontrollable catalytic uncontrollable nature of the reaction, manner to a relatively high temperature, e. g., the hazard would increase as the nitrobenzene is around 300° C. This results in vigorous and raised to a large excess over the aniline, if the more or less complete vaporization of the remain inert solvent were not employed. But when an ing unreacted nitrobenzene and aniline as well as inert diluting solvent is employed, a large excess the production of objectionable by-products. In 55 of nitrobenzene can be used without such danger 2 2,332,179 and With the combined advantages of the inert phenazine oxide in aromatic solvents such as ben Solvent and of the excess of nitrobenzene, includ Zene, particularly When hot, is Such that it Will ing high yelds of phenazine oxide, and minimizing largely or entirely remain in Solution, when Sufi or prevention of the formation of azobenzene and cinet solvent is employed. Phenazine oxide is of other objectionable by-products such as car less Soluble in cold benzene and, if the reaction bon, tar and ammonia. As a result it is possible mixture is cooled, some of the phenazine oxide to produce a raw phenazine oxide product which may be precipitated. In the case of straight is free or relatively free from objectionable in chain hydrocarbons, such as hexane and ligroin, purities and which, when suitably separated from which have only a limited solubility for phena the reaction mixture is of Sufficient purity to be zine oxide, this product will be largely present aS used directly and without further purification; a Solid in the reaction mixture. When a Con and the phenazine produced therefrom can be siderable excess of nitrobenzene is used this has Similary U.Sed. a solvent action on the phenazine oxide and, even the proportions of nitrobenzene and aniline with straight chain hydrocarbon solvents, the used in the process can be varied; and certain of presence of the excess nitrobenzene Will hold part the advantages of the process can be obtained of the phenazine oxide in solution, particularly at With the use of an inert Solvent and even higher temperatures. though a large excess of nitrobenzene over ani The present invention provides various methods line is not employed. In general, however, at of Working up the reaction mass and of Separat least one mole of nitrobenzene will be employed 2 ing the phenazine oxide therefrom. In general, for each mole of aniline; and an excess of nitro the reaction mixture ºor Slurry, consisting of Sol benzene is advantageously employed. Even With vent, dissolved constituents and in Soluble cake, is equal molar proportions of nitrobenzene and filtered to separate the dissolved and insoluble aniline considerably better yields of phenazine constituents. When an aromatic solvent Stich as oxide and smaller yields of undesirable azoben- 2. benzene is employed, and the slurry is filtered zene may be obtained, When an inert solvent is hot, the phenazine oxide will be largely contained employed. As the molar excess of nitrobenzene in the hot solution and can be advantageously increases the yield of phenazine oxide is found separated therefrom by extraction. With an acid to markedly increase and the yield of azobenzene solution, such as 15% to 20% aqueous hydro to markedly decrease. For example, with equal it chloric acid solution, to remove the dissolved molar quantities of nitrobenzene and aniline, and phenazine oxide and leave behind a Zobenzene and With the use of an inert solvent, I have obtained excess nitrobenzene in the solvent. The Solvent yields of around 30% of phenaZene oxide based and dissolved constituents can then be advan on the aniline employed; while by increasing the tageously returned to the process for reuSe until nitrobenzene to about 2 moles for each mole of : such time as the amount of azobenzene increases aniline the yield of phenazine oxide has been to the point where it is desirable to subject the around 50% based on the aniline; and with a solvent to distillation to separate the azobenzene. molar proportion of around 4 to 8 moles of nitro When a solvent such as hexane or ligroin is em benzene to one of aniline I have obtained around ployed, in which phenazine oxide has only a 65 to 70% or more of the phenazine oxide, based 4 limited solubility, the solvent and dissolved Con on the aniline. The quantity of finely ground stituents separated from the slurry or reaction potassium hydroxide required for the condensa mixture by filtration can be directly returned to tion can be materially reduced when an inert the process for further use, without extracting solvent is employed, as compared with the amount the phenazine oxide from it; although if a Suffi required when such solvent is not used.