GB2170195A

GB2170195A - Sulphonation of substituted nitrobenzenes

Info

Publication number: GB2170195A
Application number: GB08502080A
Authority: GB
Inventors: Karl Fuger; Petr Stahala
Original assignee: Sandoz AG
Current assignee: Sandoz AG
Priority date: 1985-01-28
Filing date: 1985-01-28
Publication date: 1986-07-30
Also published as: GB8502080D0; GB2170195B

Abstract

A process for the preparation of a compound of formula <IMAGE> (in which either R1 is hydrogen and R2 is chlorine or R2 is hydrogen and R1 is methyl or chlorine), comprises sulphonating a compound of formula II <IMAGE> (where R1 and R2 are defined above) with sulphur trioxide in the presence of a sulphone-production inhibitor and in the absence of an inert gas or additional solvent for the sulphur trioxide. The sulphone-production inhibitor is selected from ammonium sulphate, ammonium bisulphate, sodium carbonate, potassium carbonate and sodium and potassium salts of compounds of formula I.

Description

SPECIFICATION A process for the sulphonation of substituted nitrobenzenes The invention relates to a process for the preparation of a compound of formula I

in which either R1 is hydrogen and R2 is chlorine or R2 is hydrogen and R1 is methyl or chlorine the process comprising sulphonating a compound of formula 11

where R1 and R2 are defined above; with sulphur trioxide in the presence of a sulphone-production inhibitor selected from ammonium sulphate, ammonium bisulphate, sodium carbonate, potassium carbonate and the sodium and potassium salts of compound of formula I and in the absence of an inert gas or additional solvent for the sulphur trioxide.

The preferred inhibitors are ammonium sulphate and sodium carbonate. The inhibitors are preferably used in a small amount, more preferably 0.1 to 10 mol %, most preferably 2 to 4 mol % with respect to the compound of formula 11.

Preferably the compound of formula II used in the process of the invention is 1-methyl-2-nitrobenzene or 1-chloro-2-nitrobenzene.

The molar amount ofsulphurtrioxide used per mol of compound of formula II in the process of the invention is so chosen as to hinder, as far as possible, the formation of a disulphonated product. The preferred molar amount of sulphur trioxide (per mol of compound of formula II) is 0.1 to 1.5, more preferably 1.1 to 1.4. For the sulphonation of 1-methyl-2-nitrobenzenethe preferred molar amount (per mol of compound of formula II) of S03 is 1.05 to 1.10 and for the sulphonation of 1 -chloro-2-nitrobenzene and 1-chloro-4-nitrobenzene 1.2 to 1.4.

The sulphurtrioxide is preferably added in liquid form. The sulphonation occurs so quickly that practically all the sulphur trioxide is absorbed at once. When the amount of sulphur trioxide used is in the range 1 to 1.5, conversion can be achieved to produce yields of 80 to 100 % without sulphone-production or disulphonation occurring to any significant extent.

Sulphonation may be carried out under normal pressure or at slightly reduced or increased pressure, for instance 0.5 to 3 bar. However, the normal pressure of 1 bar is simplest and more preferred.

The reaction temperature is practically above the boiling point of sulphur trioxide but it is preferred that the reaction temperature is controlled so that it does not rise above 1 50 C (the sulphonation reaction being exothermic). More preferably the reaction is controlled so that it does not rise over 1 20 C. It is preferable that the reaction temperature is in the range 60 to 1 50 C, more preferably 95 to 1 20 C, most preferably 99 to 105"C.

The rate of reaction is preferably controlled by the reaction temperature, which in turn is controlled preferably by the addition ofsulphurtrioxide in controlled dosages and with cooling.

The compounds of formula I, when prepared according to the invention, have good yields and purity.

After termination of the reaction, the reaction mixture may be poured into water or onto ice or into a mixture of water and ice. The resulting mixture is then filtered with the aid of activated charcoal or filtering earth if desired. The aqueous solution contains the sulphonated product and can be used directly in this form for further reaction or the product can be obtained from the solution, either by salting out or by neutralising with the addition of base and then precipitating, followed by conventional filtration and drying. The product is then at least partially in salt form.

The compounds of formula I can be converted to a salt form i.e. to compounds of formula III

where R1 and R2 are defined above and M is an alkali or alkaline earth metal cation, by reacting the compounds of formula I with an alkali- or alkaline earth metal-yielding base.

Preferred significancesfor M in the compound of formula I are lithium, sodium, calcium, potassium, barium and magnesium, the most preferred significance being potassium.

The compounds of formula I and III are useful as intermediates for the formation of amines of the formula IVto VIII.

These compounds in turn are useful in the preparation of dyestuffs.

The invention will now be illustrated by the following Examples in which all parts and percentages are by weight and all temperatures are in "C.

Example 1 274.1 Parts of o-nitrotoluene are placed in a sulphur trioxide-resistant reaction vessel and then 6.8 parts of ammonium sulphate are added whilst mixing. The mixture is heated to 1000 and 176 parts of liquid sulphur trioxide are introduced over a 45 minute period whilst stirring well. Heating of the mixture is discontinued and the sulphur trioxide introduction is so regulated to keep the temperature of the mixture at 1020 i 2.5 .

After all the sulphur trioxide has been added the temperature is raised to 1100 and the mixture is stirred for a further 3 hours. The sulphonated product is then poured into a mixture of 100 parts of water and 300 parts of ice and the reaction vessel is washed out with 300 parts of water. The two aqueous phases are then added together (the temperature being about 30 ). After adding 4 parts of filtering earth the mixture is filtered and the filter residue is washed with 80 parts of water. The two filtrates are then added together. The resulting approximately 33.6 % aqueous solution contains 409.6 parts of 1-methyl-2-nitro-benzene-4-sulphonic acid with a yield of 94.3% of theory.

The resulting aqueous solution may be used as it is or the sulphonated product may be salted out and if desired also neutralised.

Example 2 157.5 Parts of o-chloronitrobenzene are placed in a sulphurtrioxide resistant reaction vessel and then 3.4 parts of ammonium sulphate are added whilst mixing. The mixture is then warmed to 1000 and to the resulting melt 108 parts of liquid sulphur trioxide are introduced over a period of 45 minutes whilst stirring well. Heating of the mixture is discontinued and the sulphurtrioxide introduction is so regulated to keep the temperature of the mixture at 1020 t 2.5 .

After all the sulphur trioxide has been added the temperature is raised to 1 10" and the mixture is stirred for a further 2 hours. The sulphonated product is poured into 250 parts of cold water and the reaction vessel is washed out with 100 parts of water. The two aqueous phases are added together and after adding 1 part of filtering earth and 1 part of activated charcoal, 140 parts of ice are added and the mixture is stirred for a further 15 minutes (the temperature of the mixture being then about 30 ). This is then filtered and 212 parts of a 50 % solution of potassium hydroxide are then added whilst at the same time cooling the mixture. The pH of the solution rises to about 7 and the temperature of the neutralised mixture is about 40".

After stirring for a further two hours the solid product is filtered and pressed.

216.7 Parts of 1-chloro-2-nitrn-benzene-4-sulphonic acid (in potassium salt form) result which is a yield of 91.2 % of theory.

Example 3 By analogy with Example 2, p-nitrochlorobenzene may be sulphonated to 1-chloro-4-nitrobenzene-2sulphonic acid.

Claims

1. A process for the preparation of a compound of formula I

in which either R1 is hydrogen and P2 is chlorine or R2 is hydrogen and R1 is methyl or chlorine the process comprising sulphonating a compound of formula 11

where R1 and R2 are defined above; with sulphur trioxide in the presence of a sulphone-production inhibitor selected from ammonium sulphate, ammonium bisulphate, sodium carbonate, potassium carbonate and the sodium and potassium salts of compounds of formula I and in the absence of an inert gas or additional solvent for the sulphur trioxide.

2. A process as claimed in Claim 1, in which the sulphone-production inhibitor is ammonium sulphate or sodium carbonate.

3. A process as claimed in Claim 1 or Claim 2 in which the temperature of the reaction is in the range 60 to 150"C and the pressure is in the range 0.5 to 3 bar.

4. A process as claimed in any one of the preceding claims in which the sulphur trioxide is added in liquid form.

5. A process as claimed in any one of the preceding claims in which the molar amount of sulphur trioxide used, per mol of the compound of formula II, is from 0.1 to 1.5.

6. A process as claimed in any one of the preceding claims in which the molar amount of the inhibitor used is 0.1 to 10 mol % with respect to the compound of formula II.

7. A process as claimed in any one of the preceding claims in which the compound of formula II is 1 -ch lo ro-2-nitrobenzene or 1 -methyl-2-nitrobenzene.

8. A process as claimed in Claim 1, for the preparation of a compound of formula Ill

where R1 and R2 are defined in Claim 1 and M is an alkali metal or alkaline earth metal, the process comprising the additional step of reacting a compound of formula I with an alkali- or alkaline-earth metal-yielding base.

9. A process as claimed in Claim 8 in which M is selected from lithium, sodium, potassium, calcium barium and magnesium.

10. A process according to Claim 1 as described in any one of the Examples.