US2136187A - Nitration of para cresol - Google Patents

Description

Patented Nov. 8, 1938 UNITED STATES PATENT OFFICE NITRATION OF PARA C'RESOL No Drawing. Application April 5, 1937, Serial No. 135,107

11 Claims.

Our present invention relates to the nitration of para cresol to form meta nitro para cresol, expressed as 4-methyl-2-nitro-l-hydroxy-benzene.

Some compounds are readily nitrated by well known procedures, while others are not subject to such procedures owing to numerous undesired results, such as isomeric nitration, di-nitration, oxidation, resinification, or owing to the effect of the procedure upon impurities or isomers accompanying the desired raw material.

Para cresol as such is a fairly expensive raw material, but when mixed with its meta isomer roughly in the proportion of parts meta to 40 parts para, it is a much less expensive material. At considerable cost for treatment, the content of the meta isomer may be reduced. Considering costs, yields, purities, kinds of nitration processes, and commercial supplies, specifications, and demands, there is still a place for a low-cost nitrating process operable upon either a pure para cresol or upon an impure para cresol, such as one containing its isomeric forms, particularly the meta cresol, to yield an acceptable grade of meta nitro para cresol.

Para cresol has heretofore offered practical and economic difiiculties for low-cost nitration processes. So far as we have been able to ascertain, a complicated procedure has been employed heretofore, involving use of solvents, such as ether, and a necessary cooling. The nitration of cresol offers difliculties not encountered in nitrating phenol. While there is but one form of phenol, there are three isomeric forms of cresol. These may or may not react differently to some selected nitration procedure. A procedure which nitrates one isomer may not nitrate another; and where mixed isomers are present, one isomer may interfere with nitration of another isomer.

The present invention aims to provide a simple practical and economic process for the nitration of para cresol, which may be practiced upon a pure para cresol, and also upon mixed cresol isomers to nitrate the para cresol content, and to give in both cases a useful grade of meta nitro para cresol.

A particular object of the invention is the aqueous nitration of cresol containing para cresol by the action of an aqueous solution of nitric acid to secure the desired nitration of the para cresol content.

A further object of the invention is the aqueous nitration of cresol containing para cresol by the action of a nitration mixture derived from sulphuric acid and a nitrate salt, and used with considerable water.

Various other and ancillary objects and advantages will hereinafter become apparent.

We have discovered that our process is selective in that it effects nitration of para cresol, but does not likewise nitrate isomeric cresols. When our invention is practiced upon pure para cresol, it gives a clean product and a suitably high yield. However, when mixed isomers are used, such as one containing para cresol and 15% meta cresol, the reaction mass exhibits considerable oxidation and formation of tar or resin, without seriously altering the expected yield of meta nitro para cresol based on the actual content of para cresol initially employed. Further, we have found that the process does not nitrate pure ortho cresol or pure meta cresol in any smooth manner comparable to its nitration of pure para cresol. Therefore, we may use our process for nitrating either a pure para cresol or a mixture of cresol isomers, to obtain nitration of the para cresol isomer without similar or interfering nitration of the other isomers. Although products of oxidized or resinified character may be produced by the process from meta or ortho isomers, or from minor reaction on the para isomer, these only create mechanical difficulties having to do largely with the recovery and purification of the desired meta nitrated para cresol. The extent of these difficulties will therefore in part determine how much impurity may attend the para cresol in the original cresol, and also determine to what extent the preferred process may be varied within the permissible limits set forth. We have found it very practicable to nitrate either pure para cresol, or an impure para cresol containing as much as 15% of the meta isomer, without materially changing the yield or efficiency of the procedure based upon the chemical conversion of the actual content of pure para cresol. Purification of commercial 60-40 mixed isomers to a point where composition is roughly 85% or more of para cresol and 15% or less of meta cresol is feasible and economically practicable for the present procedure. And likewise the present procedure is practicable for such an impure para cresol.

The process is distinctive in being carried out as an aqueous nitration and by contact in a two-phase mixture with the cresol employed, para cresol being not completely if at all soluble in the aqueous nitrating solution. As practically carried out, a dilute sulphuric acid solution containing nitric acid is formed. This may be done in various ways as by adding nitric acid to dilute sulphuric acid, or adding a nitrate salt to a strong or dilute sulphuric acid, and diluting if required. Practically, an excess of a strong sulphuric acid and sodium nitrate are mixed. This forms nitric acid, sodium acid sulphate, and a weaker sulphuric acid. This mixture is then poured into water, or into mixed ice and water, to give quickly and directly a sufficiently cool nitrating liquid for the process. Then with heavy agitation, the pure or impure cresol is slowly added in small stream, dropwise, or like manner over an extended period to assure good mixing, such as an hours time more or less, dependent upon the character of apparatus and the agitation. The time is not a critical factor, The two-phase mixture resulting, is further agitated to assure completion of the reaction, and a period of two hours agitation after completion of the mixture is suitable. This time period is not critical with a suflicient agitation to assure good nitrating contact to complete the reaction. A heavy oil layer is then allowed to settle to the bottom, which layer is separated from the upper layer, washed, and purified, preferably through a vapor phase as a distillate by steam distillation. This is the desired meta nitro para cresol.

The temperature of the reaction may be from C. to 60 C. Preferably it is lower at the beginning so that any increase by heat generated may keep it below the prescribed limit. It is further preferred to keep the temperature between 30 C. and 40 C. Lower temperature seems to extend the time of nitration reaction, permitting side reactions to proceed too far, and this is more noticeable as the acid concentration is greater.

The following specific example gives a range of proportions of materials which may be employed.

Example 1 Parts by weight Sodium nitrate (or equivalent potassium nitrate) 120 to 125 92% sulphuric acid 450 to 480 Water (600 parts ice) 400 to 4000 Pure or crude para cresol 108 "lm-l'liw ll 01mwhere water is 1400 to 1000 parts.

The foregoing formula is based upon 108 parts of the para cresol being a molecular quantity, or 1 mol of cresol. It may contain, for example 15% of admixed meta isomer, and the 108 parts or the formula may be calculated upon the mixed isomers or upon the content of the para isomer. The amount of sodium nitrate or equivalent nitric acid set forth is about 1.4 to 1.5 mols for the 1 mol of cresol to be nitrated and therefore there is an excess of nitric acid available for loss and for side reactions not desired. The amount of sulphuric acid is roughly 4.2 to 4.5 mols, and only about 1.4 mols of this is lost as free acid in generating 1.4 to 1.5 mols of nitric acid from the nitrate salt. Excess sulphuric acid no doubt serves at this low dilution as the usual nitration catalyst. The large amount of water is necessary to minimize resinification and oxidation arising from any undesired side reactions which may occur. The water item of the formula is from about 20 to about 220 mols to which about 2 mols are added by the sulphuric acid item of the formula, and another mol of water is created in the nitration, such additions having practically no effect. Below 25 C. the nitration proceeds very slowly. Above 60 C. certain ingredients of the mass burn up or are destroyed. The best results are obtained by following the procedure as given above, within the preferred temperature limits of 30 C. to 40 C. and with 1400 to 1600 parts of Water, which is from 78 to 89 mols of water. Considering the added water above mentioned the preferred nitrating acid solution contains roughly from 80 to 90 mols of water for at least 1 mol of nitric acid, and a small amount of free sulphuric acid. A yield of 80% to 85% of meta nitro para cresol is thus obtained based upon the actual para cresol originally present in the raw material.

However, it is to be understood that variations are permissible as will be shown from the following tabulated examples, using a fixed quantity of 480 parts of 92% sulphuric acid, 125 parts of sodium nitrate, 108 parts of cresol, and the variations as follows:

Based on content of para cresol.

The process is of great practical merit because it is applicable to both pure para cresol, and to mixed isomers containing para cresol, without change of procedure. Its selective action, in nitrating the para isomer and in not similarly nitrating the ortho and meta isomers, makes it a valuable procedure in that the product of using mixed cresols is relatively free from mixed nitrated isomers resulting from simultaneous nitration of the mixed cresol isomers. For the economic use of the process, the practical limits of para cresol in mixed cresol isomers may be fixed by many conditions entirely independent of the invention. It will thus appear to those skilled in the art, that the invention may be used in various ways with great chemical advantage as an isolation procedure for para isomeric compounds within the scope of materials involved, and with great economic advantage according to raw materials available, and other economic factors.

We claim:

1. A process for the nitration of para cresol to form meta nitro para cresol, which comprises subjecting up to 1 mol of such cresol to the action of an aqueous nitrating acid solution having at least 1 mol of nitric acid, free sulphuric acid, and from 20 to 220 mols of water, said action being conducted at a temperature from 0 C. to 60 C.

2. A process for the nitration of the para cresol content of mixed cresol isomers to form meta nitro para cresol, which comprises subjecting up to 1 mol of such mixed cresol isomers to the action of an aqueous nitrating acid solution having at least 1 mol of nitric acid, free sulphuric acid, and from 20 to 220 mols of water, said action being conducted at a temperature from 0 C. to 60 C.

3. A process for the nitration of para cresol to form meta nitro para cresol, which comprises subjecting up to 1 mol of such cresol to the action of an aqueous nitrating acid solution having at least 1 mol of nitric acid, free sulphuric acid, and from 20 to 220 mols of water, said action being conducted at a temperature from 30 C. to 40 C.

4. A process for the nitration of the para cresol content of mixed cresol isomers to form meta nitro para cresol, which comprises subjecting up to 1 mol of such mixed cresol isomers to the action of an aqueous nitrating acid solution having at least 1 mol of nitric acid, free sulphuric acid, and from 20 to 220 mols of water, said action being conducted at a temperature from 30 C. to 40 C.

5. A process for the nitration of para cresol to form meta nitro para cresol, which comprises subjecting up to 1 mol of such cresol to the action of an aqueous nitrating acid solution having at least 1 mol of nitric acid, free sulphuric acid, and from 80 to 90 mols of water, said action being conducted at a temperature from 30 C. to 40 C.

6. A process for the nitration of the para cresol content of mixed cresol isomers to form meta nitro para cresol, which comprises subjecting up to 1 mol of such mixed cresol isomers to the action of an aqueous nitrating acid solution having at least 1 mol of nitric acid, free sulphuric acid, and from 80 to 90 mols of water, said action being conducted at a temperature from 30 C. to 40 C.

7. A process for the nitration of para cresol to form meta nitro para cresol, which comprises subjecting up to 1 mol of such cresol to the action of an aqueous nitrating acid solution consisting of the reaction products of at least 1 mol of a nitrate salt, at least about 4 mols of sulphuric acid calculated as 100%, and from 20 to 220 mols of water, said nitration being conducted at a temperature from 0 C. to 60 C.

8. A process for the nitration of the para cresol content of mixed cresol isomers to form meta nitro para cresol, which comprises subjecting up to 1 mol of such mixed cresol isomers to the action of an aqueous nitrating acid solution consisting of the reaction products of at least 1 mol of a nitrate salt, at least about 4 mols of sulphuric acid calculated as 100%, and from 80 to 90 mols of water, said nitration being conducted at a temperature from 30 C. to 40 C.

9. A process for nitrating para cresol to form meta nitro para cresol which comprises mixing para cresol with an aqueous nitrating acid solution containing sulphuric acid at from 0 C. to 60 C. whereby para cresol is converted to meta nitro para cresol as an oil in the spent nitrating acid solution, separating said oil from the said spent acid solution, and purifying the separated oil through its vapor phase.

10. The method of making a separation of a para compound from accompanying isomeric compounds which consists in subjecting a mixture of isomeric cresols containing a substantial amount of para cresol to the action of an aqueous nitrating acid solution containing sulphuric acid at from 0 C. to 60 C. whereby para cresol is converted to meta nitro cresol as an oil in. the spent nitrating acid solution and the isomeric cresol is largely converted to tar or resinous matter, and separating the tar and resinous matter from the meta nitro para cresol.

11. The method of selectively treating para cresol in the presence of an isomeric cresol to form meta nitro para cresol substantially free from isomers, which consists of subjecting the isomeric cresols to the action at from 0 C. to 60 C. of an aqueous nitrating solution containing sulphuric acid, the action of the nitrating solution being selective to nitrate the para cresol isomer, and to convert the isomeric cresol into waste matter separable from the resulting meta nitro para cresol.

ROBERT FRYE. GRADY M. ONEAL.