US2413507A - Process for the manufacture of dibenzanthronyls - Google Patents

Description

Patented Bee. 31, 1946 UNITED STATES PA'rsNr orrlce PROCESS FOR THE MANUFACTURE OF DIBENZANTHRONYLS Henry R. Lee, Pitrnan, N. J., and Edward T. Howell, Wilmington, Del, assignors to E. I. du'Pont de Nemours & Company, Wilmington, Del a corporation of Delaware No Drawing. .Application March 27, 1946, Serial No. 657,612

This invention relates to an improvement in the process of the manufacture of dibenz'anthronyls, andtmore particularly, to an improved process for carryingout the c'ondensationof benzanthrone and its simple substitution derivatives to Bz-1:Bz- Y-dibenzanthronyls'.

In the Conversion of benzanthrone to 32-1132- l-dibenZanthronyl, the condensation has heretofore been carried out i'riconcentrated sulfuric acid by means" of an oxidizing agent such as manganese dioxide, chromic acid, etc. The conversion, as originally described in German Patent 431,774; was exceptionally low,' and a high per centage of oxidation products were produced, It was later found that; if the condensation was carried out under more mild conditions and stopped at a point where from 36% to 40% of benzanthrone remaine' d' unchanged in the reaction mass, a higher totalconversion to 332-1 :32- l"-diben'zant'hronyl could be obtained. This-prom ess, however, requires the recovery of the benzanthrone if comparatively high yields of the Bz-i:Bz-1-dibenzanthronyl are to beobtained based on the total benz'anthrone' employed;

Irrespective of how the oxidation of the benzant-hrone has heretofore been carried out, side react-ions inevitably takeplace which produce oxo-derivative's of bothbenzanthrone and dibenzant-hrcnyl, and these remain as impurities in the final product. On reduction of these oxoderivatives, such as with sulfurous acid, they are in the main converted to h-ydroxy compounds which will be referred to hereaftergenerally as oxy bodies. A description of these o-xy bodies may be found in Examples 1 and 4 of British Patent 251,313. While some of the oXy bodies are soluble in aqueous alkaline solutions, others, although apparently forming alkali metal salts, are not sufli'ciently soluble to be removed by an alkali'ne extraction, and it has'been found that certain of the oxy derivatives'of Bz-1:B'z--1'-dibenz anthronyl were-notremoved by previous methods of separation and were therefore present with the Bz-lzBz-l -dibenzanthronyl as a mixture which has heretofore been mistaken for the 32-1 :Bz-l -dibenzanthronyl itself.

It is an object of the present invention to provide an improved process for the preparation of 182-1 :Bz-1'-dibenzanthronyl and its simple monovalent substitution derivatives, whereby higher yields of the Bz-l:Bz-l-dibenzanthrony1 are obtained and the amoLmt of oxy-bodies as impurities is materially reduced.

We have now found that, where alkyl sulfuric acids are used in place of sulfuric acid as the sol- 2 Claims. (01. 260'36 3) vapor reaction medium, much higher yields of the Bz-l:Bz-l -dibenzanthronyl of a higher purity are obtained than has heretofore been possible without reworking the unchanged benzanthrone, which offers difficulties on a commercial scale, The, alkyl sulfuric acids are preferably the methyl sulfuric acid and ethyl sulfuric acid. When using these alkyl sulfuric acids, as little as from 5 to '7 parts of the alkyl sulfuric acid may be employedper part of benzanthrone to be oxidized. Larger proportions may be employed, al-

though the use of unnecessarily large amounts will, of course, make the process less economical.

The oxidizing agents employed are those which have previously been used with sulfuric acid, such as manganese dioxide and chromic acid anhydride. used Will be varied, depending upon the amount of solvent employed, although usually it will be found that from 3 to 5 mols of manganese dioxide (106% pure basis) per mol' of benzanthrone will give a satisfactory conversion of the benzanthrone to the dibenzanthronyl The oxidation is preferably carried out at temperatures of from 5 to 20 C., although lower or higher temperatures may be employed.

The alkyl sulfuric acid is preferably made as a preliminary step in carrying out the oxidation of the benzanthrone. In the preparation of the alkyl sulfuric acid by the addition of anhydrous alcohols to chlorosulfonic acid at low temperatures, there is usually present in the resulting alkyl sulfuric acid a small amount of sulfuric acid, but it has been found that the presence of this small amount of sulfuric acid is not detrimental in carrying out the oxidation of the benz anthrone, While there is also present in the alkyl sulfuric acid some residual hydrochloric acid, this can be largely eliminated by air-blowing or by blowing an inert gas through the alkyl sulfuric acid when formed. It has been found, however, that the presence of small amounts of hydrochloric acid up to 0.75% does not materially affeet the resulting oxidation reaction.

The presence of excess alcohol or water in the alkyl sulfuric acid, however, retards the subsequent oxidation of the benzanthrone and gives an unnecessarily high amount of unchanged benzanthrone in the final product. For best results, the alkyl sulfuric acid should be anhydrous and free from alcohol.

For purposes of this invention, We do not wish to be limited to any particular method of formation of the alkyl sulfuric acids.

lhe amount of oxidizing agent to be 3 The following example is given to illustrate the invention. The parts used are by weight.

Example 1078 parts of chlorosulfonic acid are charged into a closed enamel lined kettle fitted with agitator and cooling jacket. The charge is cooled to l C. and 302 parts of anhydrous methanol are slowly run in with cooling at such a rate that the temperature does not exceed 0 C. Hydrochloric acid, which is copiously evolved, is vented ofi. After all of the methano1 has been added, the temperature of the mass is raised to from 20 to'25 C. and dry air or an inert gas is blown through until only traces of hydrochloric acid come out of the vent.

1000 parts of the above methyl sulfuric acid are charged into a closed iron or steel kettle fitted with agitator and cooling bath. 200 parts of purified benzanthrone are charged in and the solution is cooled to from '-5 to 0 C. 370 parts of 81.6% manganese dioxide are added with cooling at such a rate that the temperature does not exceed C. After all of the manganese dioxide has been added, the reaction mass is stirred at from -5 to 0 C. until no further reaction takes place. This may require about 20 hours. The reaction mass is discharged into 5000 parts of water containing 370 parts of sodium bisulfite. 400 parts of concentrated sulfuric acid are added and the slurry is heated to the boil. More sodium bisulfite is added if an excess of sulfur dioxide is not detected. 5000 parts of cold water are added and the suspension is filtered off and washed acid-free. If not completely free from manganese dioxide, the filter cake is milled and given an additional bisulfite treatment with sulfuric acid, and is then filtered, washed acid-free and dried. Calculated to the ash-free basis, the average analysis shows a 70.0% yield of Bz-l :Bz- 1'-dibenzanthronyl.

A yield of 70% by this process is compared with a direct yield of from 40% to 55% of B2- 1:Bz-1'-dibenzanthronyl when the condensation is carried out according to the processes of Examples 2 or 3 of U. S. Patent 2,001,063, when the yields are calculated on the basis of an acid recrystallization and purification carried out as follows:

Ten parts of the crude Bz-1:Bz-1'-dibenzanthronyl, as obtained directly by the condensation as described above, are dissolved in 100 parts of 95% sulfuric acid at from 25 to 30 C. 28 parts of water are added at such a rate that the temperature rises gradually to 100 C., and the rate is then adjusted so that the rest of the water is added at from 90 to 100 C. The mass is allowed to cool to from 25 to 30 C. with agitation. The microscope shows rod-like crystals of a size suficient to filter rapidly. The crystals are filtered on a porous plate filter and are washed with 100 parts of 75% sulfuric acid. The crystals are digested in water, filtered, washed with water and digested in dilute caustic soda solution. The slurry is filtered, washed alkalifree and dried. The weight of this dried product, when compared with the original amount of lbenzanthrone employed in the condensation, is used as the yield of Bz-1:Bz-1'-dibenzanthronyl obtained by the process involved.

When ethyl sulfuric acid is substituted for the methyl sulfuric acid in the above example, a similar improvement in yields of a relatively pure Bz-lzBz 1'-dibenzanthronyl is obtained. The ethyl sulfuric acid employed may be produced as follows:

621 parts of chlorosulfonic acid are charged into a closed enamel lined kettle fitted with agitator and cooling jacket. The charge is cooled to -10 C. and 245 parts of absolute ethyl alcohol are slowly run in with agitation and cooling so that the temperature does not exceed 0 C. The hydrochloric acid gas evolved is vented off. When all of the alcohol has been added, the mass is allowed to warm to from 20 to 25 C. and is blown with dry air until practically free from hydrochloric acid.

6 methyl benzonthrone, 6 chloro benzanthrone, or other halogen or methyl derivatives of benzanthrone which do not contain the halogen or methyl in the 2- or Bz-l-positions, can be converted to the corresponding Bz-1:Bz-1-dibenzanthronyl in the manner illustrated in the above example. Similar improvements in yield and purity of the resulting dibenzanthronyl are obtained.

The use of methyl or ethyl sulfuric acid not only increases the yield of the desired Bz-lzBz- 1'-dibenzanthronyl but permits a material increase in the production of the dibenzanthronyl per unit of equipment, for, while with the methyl andethyl sulfuric acid only from 5 to 7 parts are required per part of benzanthrone, when using sulfuric acid as the solvent, optimum yields of the dibenzanthronyl are obtained only when at least 15 parts of sulfuric acid are employed per part of benzanthrone.

We claim:

1. In the process for preparing Bz-l:Bz-1'-dibenzanthronyl and its halogen and methyl derivatives wherein condensation of the benzanthrone compound is effected by means of an oxidizing agent, the step which comprises carrying out the condensation of the benzanthrone compound in an alkyl sulfuric acid of the class consisting of methyl sulfuric acid and ethyl sulfuric acid, the reaction being carried out at temp-eratures of from -5 to 20 C. p

2. In the process for preparing Bz-1:Bz-1-dibenzanthronyl and its halogen and methyl derivatives wherein condensation of the benzanthrone compound is effected by means of an oxidizing agent, the step which comprises carrying out the condensation of the benzanthrone compound with manganese dioxide in an alkyl sulfuric acid of the class consisting of methyl sulfuric acid and ethyl sulfuric acid, the reaction being carried out at temperatures of from -5 to 20 C.

HENRY R. LEE. EDWARD T. HOWELL.