GB2092137A - Tertiary alkyl hypohalite production - Google Patents

Abstract

A tertiary-alkyl hypohalite, in particular tertiary-butyl hypochlorite, is produced by reaction of a tertiary alkanol, halogen and an aqueous inorganic base at a temperature up to 100 DEG C and a pressure, preferably below atmospheric, to vaporize tertiary-alkyl hypohalite product thereby to remove the heat of reaction and control the reaction temperature without external cooling.

Description

SPECIFICATION Improvements in or relating to tertiary hypohalite production This invention relates to the production of tertiary-alkyl hypohalites, and more particularly to the production of tertiary-alkyl hypochlorites.

The reaction between a tertiary alkanol, chlorine and an aqueous base to produce a tertiary-alkyl hypochlorite is generally known in the art; for example from U.S. Patent Specification Nos. 1,938,175 and 3,149,140. In addition, U.S.

Patent Specification No. 4,008,133 discloses the production of tertiary-butyl hypochlorite in an overall process for producing olefinic oxides.

The reaction between a halogen, a base and a tertiary alkanol to produce tertiary-alkyl hypohalite is a highly exothermic reaction, and difficulties have been encountered in attempting to dissipate economically the heat of reaction to provide for effective temperature control. An ineffective control of the temperature can result in a decomposition of the tertiary-alkyl hypochlorite, with resulting loss of yield and a possibly uncontrollable reaction.

The object of the present invention is to provide an improved process for producing a tertiary alkyl hypohalite by reaction of a tertiary alkanol, a halogen and an aqueous base.

In accordance with the present invention there is provided a process for producing a tertiary alkyl hypohalite, which comprises reacting tertiary alkanol either with a halogen and an aqueous solution of an inorganic base or with a prehalogenated aqueous solution of an inorganic base, at such a temperature and at such a pressure that the tertiary alkyl hypohalite product is vaporized during the reaction to control the reaction temperature and to recover tertiary alkyl hypohalite as a vapour product, the said temperature being up to 1000C.

Preferably, the reaction is conducted at a subatmospheric pressure with the pressure preferably being 5 to 100 kPa, most preferably 20 to 60 kPa.

The reaction temperature is conveniently from just above the freezing point up to 1 OC C, preferably up to 600C, and most preferably from 400C to 600C. As described, the pressure is coordinated with the temperature to ensure vaporization of the hypohalite product.

In a preferred embodiment, the reaction is a continuous reaction, with the tertiary alkanol, halogen and aqueous solution of inorganic base and/or tertiary alkanol and prehalogenated aqueous base being continuously fed into a reactor, and the vaporized tertiary-alkyl hypohalite, and generally also some water vapour, being continuously withdrawn from the reactor.

The reactor may be any one of a wide variety of reactors which provide good contact between reactants, and in particular those suitable for gasliquid reactions. A deep tank type of reactor, in which the reactants are introduced into a mass of liquid comprised of the reactants stirred by the bubbles of vaporized hypohalite, is particularly simple and useful.

In a particularly preferred embodiment, the reactor is maintained in substantially corrrpiete heat balance by controlling the pressure so that substantially all of the heat developed by the chemical reaction is removed by vaporization of the tertiary-alkyl hypohalite product and generally also small amounts of water and/or alkanol. In this manner, there has been found to be no necessity to effect external cooling of the reaction medium in order to maintain reaction temperature. Thus, the reaction is effected under substantially isothermal conditions; in other words the reaction temperature does not vary by more than a few degrees centigrade throughout the reactor.

The tertiary alkanol employed as reactant is preferably tertiary butyl or tertiary amyl alcohol, with tertiary butanol being particularly preferred.

The aqueous inorganic base may be any one of a wide variety of bases including alkali metal and alkaline earth metal hydroxides, with sodium hydroxide, potassium hydroxide and calcium hydroxide being particularly preferred, and sodium hydroxide being most preferred.

The reactants may be employed in a wide variety of proportions depending upon desired reaction results. Thus, for example, if it is desired to provide for substantially complete conversion of any desired reactant, excesses of the other reactants may be used. In general, it is preferred to employ the reactants in about stoichiometric proportions; in other words about an equimolar amount. Thus, in order to minimize the presence of halogen in the hypohalite vapour product, the halogen to base molar ratio should not exceed 1.05:1. The amount of halogen in the hypochlorite vapour product can be reduced by providing one or more additional stages in which the vapours which leave the reactor are contacted with aqueous base in order to remove halogen by production of hypoha;ite.

Similarly, in order to prevent the presence of organics, such as tertiary alkanol, in the aqueous phase recovered from the reactor, the amount of tertiary alkanol to base should not be much in excess, if at al!, of stoichiometric proportions, and in some cases should be less than stoichiometric proportions. Thus, for example, the tertiary aikanol to base ratio is preferably from 0.95 :1 to 1.3 :1, and most preferably from 0.98:1 to 1.05:1.

If desirable, higher amounts of tertiary alkanol may be employed and such higher amounts have not been found adversely to affect the reaction.

Although processes in accordance with the present invention have been found to be generally applicable to the production of hypochiorites or hypobromites and hypoiodites which are sufficiently stable at the reaction conditions, the processes have been found to have particular applicability to the production of hypochlorites; in particular, tertiary butyl hypochlorite. The invention is therefore further described, by way of example, with reference to the hypochlorite.

Processes in accordance with the present invention have been found to be particularly useful in an overall process for producing olefinic oxides in which a tertiary alkyl hypochiorite is employed for production of a chlorohydrin by reaction with an olefin and water. Such a process is described in, for example, U.S. Patent Specification No.

4,008,133. Thus, in such a preferred embodiment, chlorine generated in an electrolysis cell, electrolyte obtained from the cathode compartment of the cell (which includes an aqueous solution of sodium chloride and sodium hydroxide) and tertiary alkanol are introduced into the hypochlorite production reactor which is operated at the temperatures hereinabove described, and at a pressure as hereinabove described to recover a tertiary alkyl hypochlorite as a vapour and to control the reaction temperature by removing the heat of reaction by vaporization of the tertiary alkyl hypochlorite product and some water. The aqueous phase, which is an aqueous brine solution, is recycled (after appropriate treatment, if required) to the electrolytic cell. The tertiary alkyl hypochlorite vapour is then employed in the chlorohydrination reactor, as described in U.S.Patent Specification No. 4,008,133, for production of the olefin chlorohydrin.

Alternatively all or a portion of the electrolyte may be prechlorinated, and the prechlorinated electrolyte reacted with tertiary alkanol to produce tertiary alkyl hypochlorite, which is recovered as vapour, as hereinabove described.

The invention will be further described with respect to the following Example: EXAMPLE A reactor consisted of a 2 in. (5 cm) diameter, 3 ft (0.91 m) high tube. The lower part of the tube was empty and was provided with inlets for gaseous chlorine, liquid t-butanol and an aqueous solution containing 12% NaOH and 1 5 wt /ó NaCI.

This solution simulated the cell liquor resulting from the electrolysis of approximately 25% NaCI brine.

The upper 1/2fit(0.15 m) of the tube was packed with 1/8 in. (0.317 cm) Rashing rings. The packing prevents entrainment of droplets. The outlet for the vapour reaction product was placed above the packing. In the middle of the packed region, an inlet was provided through which a stream of cell liquor could be introduced to contact the vapours leaving the reactor and thus remove from the existing gases traces of unreacted chlorine.

An outlet, placed at 12 ft (0.305 to 0.1 5 m) above the bottom of the reactor, served as an overflow for the aqueous brine, and was connected to a reception vessel. The product vapours leaving through the top of the reactor were condensed in two cold traps in series (icewater and dry ice). The last cold trap was connected to a vacuum pump.

The column was electrically traced for heating purposes and was provided with the instrumentation required for vacuum operation.

A run was started by introducing in the reactor 600 cc of 25 wt% NaCI brine. The temperature was brought to 450C and a pressure of 37 kPa (280 Torr absolute) was established.

By means of metering pumps, a stream of .1 ml/min (10.5 mmole/min) of t-BuOH and of 3.05 ml/min cell liquor solution was fed to the reactor. Gaseous chlorine (270 ml/min, 11 mmoles/min) was sparged in the liquid of the reactor. About 80% of the cell liquor was fed at the bottom of the reactor while the rest was pumped in the packed zone.

The molar ratio between the reagents was maintained at 1 .0-t-BuOCl/1 .04 NaOH/1 .05 Cl2.

The contents of the reactor were mixed violently by the bubbles which were formed. By maintaining the pressure at the indicated value, no problem was encountered in avoiding the overheating of the reaction mixture.

No liquid organic phase was observable in the reactor.

At the end of the test, the content of the traps was analyzed. The organic phase consisted of substantially puret-BuOCI.

Processes in accordance with the present invention have been found to be particularly advantageous in that they have permitted the production of tertiary alkyl hypochlorite while economically controlling the temperature to prevent a possible runaway reaction. In addition, such a result has been accomplished without necessitating external cooling of the reactants and/or reactor.

Claims (11)

1. A process for producing a tertiary alkyl hypohalite, which comprises reacting tertiary alkanol either with a halogen and an aqueous solution of an inorganic base or with a prehalogenated aqueous solution of an inorganic base, at such a temperature and at such a pressure that the tertiary alkyl hypohalite product is vaporized during the reaction to control the reaction temperature and to recover tertiary alkyl hypohalite as a vapour product, the said temperature being up to 1000C.

2. A process according to claim 1, wherein the reaction pressure is below atmospheric pressure.

3. A process according to claim 1 or 2, wherein the halogen is chlorine to produce tertiary alkyl hypochlorite.

4. A process according to any one of the preceding claims wherein the reaction is effected at such a pressure as to remove the heat of the reaction by vaporization whereby the reaction temperature is controlled to provide substantially isothermal conditions without external cooling.

5. A process according to any one of the preceding claims, wherein the tertiary alkanol is tertiary butanol.

6. A process according to any one of the preceding claims, wherein the pressure is from 5 to 100 kPa.

7. A process according to any one of the preceding claims, wherein the reaction temperature is from 400C to 600 C.

8. A process according to any one of the preceding claims, wherein the reactants are continuously introduced into a liquid comprised of the reactants which is stirred by bubbles of vaporized hypochlorite, and vapour containing hypochlorite is continuously recovered.

9. A process according to any one of the preceding claims, wherein the base is potassium hydroxide, sodium hydroxide or calcium hydroxide.

10. A process for producing a tertiary alkyl hypohalite substantially as herein described with reference to the Example.

11. A tertiary-alkyl hypohalite whenever obtained by a process according to any one of the preceding claims.

1 2. Tertiary-butyl hypohalite whenever obtained by a process according to any one of the preceding claims.

1 3. Any novel feature or combination of features described herein.