DE2632565A1 - Reacting aromatic cpds. e.g. phenol with chlorine - and recycling unreacted chlorine to reactor - Google Patents

Abstract

In the reaction of aromatic cpds. with Cl2, the unreacted Cl2 is recycled to the reactor. The effluent gases are admixed with fresh Cl2 and recycled to the reactor. The aromatic cpd. may be used in the pure form, as a melt, a soln. or suspension in an inert medium. Used for processes requiring substantial excesses of Cl2 e.g. nuclear chlorination processes, the substitution of an H atom, linked to an aromatic ring, by Cl, and in oxidation reactions, e.g. prepn. of prechlorinated quinones. Pref. starting materials for the chlorin atoms are hydrocarbons opt. substd. by inert substituents, pref. phenols, and the reactions are effected pref. without excess pressures.

Description

Implementation of aromatic compounds with chlorine

The reaction of aromatic compounds with gaseous chlorine will usually carried out with an amount of chlorine that the occurrence of unreacted Avoids chlorine in the exhaust gas. Many reactions with chlorine, especially the production higher chlorinated prevention, but only works satisfactorily if a high excess of chlorine is used. If the chlorine conversion is incomplete, the Chlorine-containing exhaust gases are passed through fresh raw material, in which the excess Chlorine is consumed. This process is used in both continuous as well as used in discontinuous processes (Ullmanns Encyclopedia of Technical Chemie, 4th edition, Volume 9, pages 505, 508 and 520). In practice, however, it is necessary to connect more than one such postreactor after the conversion vessel, in order to also collect the chlorine contained in the exhaust gas from the post-reaction vessel. In particular in the case of selective chlorination, the contents must then be worked up these post-reactors require considerable effort.

It has now been found that a process for converting aromatic compounds with chlorine it is particularly easy to do that reacted chlorine is returned to the reaction vessel. Particularly beneficial is this inventive method in such 'processes that only under one run off considerable excess of chlorine. In this case, the exhaust gas, if necessary after separation of others Products, such as the one by the Substitution of hydrogen atoms resulting hydrogen chloride, after replenishment the used amount is fed back into the l <eaction vessel by fresh chlorine.

In the process according to the invention, there may be sicl- uia an 'ivernchlorierung, thus the substitution of a hydrogen atom bound to an arnatic nucleus act through chlorine, or an oxidation reaction, for example the production of perchlorinated quinones.

The reactions according to the invention preferably proceed without application of overpressure; it is only that for feeding in the chlorine through a nozzle or an inlet pipe required minimum static overpressure required. So there are on the one hand, no pressure-resistant equipment is required, on the other hand, it allows pressureless Reaction conduct in a simple manner selective chlorination, without the usual technical effort to avoid foam nuisance. Since at any time the required If excess chlorine can be maintained, the reaction times are short. The pressure, which can easily be kept constant, also provides a specific reaction control enabled, so that the products can be obtained in high purity. There too no effort whatsoever with the post-chlorination of the contents of the post-reactors that were customary up to now is required, the process is extremely economical, especially none Separation of the chlorine from the exhaust gas is required.

The aromatic compound to be reacted with the chlorine can be used in pure Form, optionally in the form of a melt, or else in solution or suspension be in an inert medium. The method for producing such is preferred Compound used in which the highest under the respective reaction conditions Chlorination stage or the production of a Perclorverbindungen is sought. Such a preferred embodiment of the invention consists, for example, in the Chlorination of Phenol to 2,4,6-trichlorophenol and its others Conversion to tetrachloro-1,4-benzoquinone: From Fiat Final Report 1313 I, page 78 ff it is known that in the production of tetrachloro-1,4-benzoquinone to achieve a maximum yield of the initially 10 to 20% excess chlorine to over 100% must be increased. When a chlorine absorption between about 50 and 80% of the stoichiometric value decreases the speed of the up to then high Chlorine uptake decreases rapidly and approaches asymptotically despite the high chlorine excess the final value. A mixture of sulfuric acid is used as the reaction medium for the last stage and chlorosulfonic acid is used, is pressureless in the case of the invention Reaction conduct also the dreaded when releasing the pressurized Solution of the chlorine avoided foam formation.

The reaction procedure according to the invention is the same for all reactions above type applicable. Preferred starting materials are the unsubstituted ones or hydrocarbons substituted by inert radicals, preferably the phenols.

Example 1: 4 mol of phenol are placed in the reactor (3; FIG. 1) and warmed.

When the temperature has reached 70 ° C, chlorine is released from the steel bottle (1) initiated via the washing device (2). The outflowing gas is in the absorption unit (4} and cooler (5) passed over a strongly agitated water surface, the formed Hydrogen chloride is completely absorbed. The diaphragm pump (7) now pumps it over the drying devices (6; 8) flowing excess chlorine back into the reactor (3). The ratio of returned gas to freshly fed in chlorine gas is between 2: 1 and 6: 1, preferably between 4: 1 and 5: 1.

The reaction temperature in (3) is kept at 900C by external cooling, whereby the pressure in the closed system (3) / (5) is increased by the pressure compensation unit (9) levels off at the external pressure.

After the reaction has ended, the chlorine is fed in first and then the Umpumpvorrich.tlng shut down. Virtually pure 2,4,6-trichlorophenol is obtained theoretical yield. The chlorine consumption is only 1-00 to 101% of the theoretical value, while according to the known methods between 110 and 160% of the theoretically required chlorine at 2 to 4 times the time required.

Example 2t In the reactor (3) a mixture of 1200 g 100% sulfuric acid and 300 g of chlorosulfonic acid, 800 g of 2,4,6-trichlorophenol were added. The mixture is heated to 100 ° C. and then the introduction of chlorine is started. The reaction is carried out analogously to Example 1. This gives tetrachloro-1,4-benzoquinone in a yield of 91.5 to 95.5% of theory.

The chlorine consumption is 103 to 109% of the stoichiometric amount, while the known processes require a chlorine input between 116 and 156% of the theoretical required value.

L e r s e i t e

Claims (4)

Claims: 1. Process for converting aromatic compounds with chlorine, characterized in that unreacted chlorine in aas reaction vessel is returned. 2. The method according to claim 1, characterized in that the implementation consists of a nuclear chlorination. 3. The method according to claim 1, characterized in that the implementation consists of an oxidation. 4. The method according to claim 1 to 3, characterized in that the Implementation takes place without pressure.