Photonitrosation of cyclododecane in chloroform in quasi-anhydrous medium

The invention relates to a process for the preparation of cyclododecanone oxide consists in photochemically reacting cyclododecane, dissolved in chloroform, a nitrosating agent and hydrogen chloride in a virtually anhydrous medium, that is to say under conditions such that the water content in the reaction medium does not exceed 1000 ppm.

The present invention relates to the field of polymers of the polyamide-12
 type obtained by polymerization of lauryllactam. It more particularly
 relates to a process for the preparation of cyclododecanone oxime
 (reaction intermediate of lauryllactam) which consists in photonitrosating
 cyclododecane in chloroform in a virtually anhydrous medium.
 The production of cycloaliphatic oximes by the photochemical route has been
 known for many years. Conventionally, a cycloalkane is reacted
 photochemically with a nitrosating agent, in particular nitrosyl chloride,
 in the presence of an excess of hydrogen chloride, at temperatures varying
 from -30.degree. C. to +40.degree. C. The oxime thus formed, in the
 hydrochloride form, is extracted from the reaction mixture, for example
 using a strong inorganic acid. This oxime is subsequently subjected to a
 rearrangement stage by the Beckmann reaction to form the corresponding
 lactam.
 The production of lauryllactam in an industrial process under continuous
 operation is dependent on several limiting factors.
 In the photonitrosation stage, the significant parameters directly related
 to the photochemical reaction are:
 the nature of the medium in which the cyclododecane is necessarily
 dissolved since the latter is solid at the normal reaction temperature
 (see, for example, DE-A-1,240,074 and GB-A-1,095,916),
 the nature of the solvent to be introduced into the reaction medium to
 increase the solubility of the oxime and thus to prevent its deposition on
 the wall of the irradiation lamps (see, for example, FR-A-1,335,823,
 FR-A-1,552,268 and GB-A-1,136,747), and
 the influence of the abovementioned solvents on the homogeneity and
 transparency of the reaction medium, which factors have a direct effect on
 the effectiveness of the light photons.
 In the abovementioned state of the art, no reference is found to the
 influence of the water content in the reaction medium.
 The Applicant Company has now found that the limitation of the water
 content in the industrial photonitrosation stage makes it possible to
 significantly increase the yield of cyclododecanone oxime and,
 consequently, to increase the profitability of the stages which are
 situated downstream, in particular the Beckmann rearrangement and the
 recycling of the acid used in the latter stage.
 A subject-matter of the present invention is therefore a process for the
 preparation of cyclododecanone oxime which consists in photochemically
 reacting cyclododecane, dissolved in chloroform, a nitrosating agent and
 hydrogen chloride in a virtually anhydrous medium, that is to say under
 conditions such that the water content in the reaction medium does not
 exceed 1000 ppm.
 The process according to the invention is carried out conventionally and
 under reaction conditions known for the photochemical nitrosation of
 cycloaliphatic compounds.
 More specifically, in order to carry out the process according to the
 invention, cyclododecane is diluted in chloroform, the solution is
 saturated with gaseous hydrogen chloride, the nitrosating agent is added
 thereto and, finally, irradiation is carried out with light.
 The moisture level in each reactant is chosen so that the overall water
 content in the reaction medium is between 50 and 1000 ppm and preferably
 250 and 600 ppm.
 The reaction is generally carried out in a reactor and the various
 reactants are introduced continuously.
 The concentration of cyclododecane in the chloroform is generally between
 0.1 and 35% by weight and preferably 20 and 30% by weight.
 The nitrosating agent is generally chosen from nitrosyl chloride, a mixture
 of nitric oxide and of chlorine, or compounds capable of forming nitrosyl
 chloride in the reaction medium, for example alkyl nitrites which react
 with hydrogen chloride. Nitrosyl chloride is preferably used.
 The addition of the nitrosating agent is adjusted so that its concentration
 in the reaction medium is between 0.1 and 25 g/l and preferably 1 and 2
 g/l.
 The hydrogen chloride is generally introduced in the form of an anhydrous
 gas, in excess with respect to the nitrosating agent. It is preferably
 employed at saturation of the cyclododecane solution.
 Irradiation is carried out by means of one or more mercury or sodium vapour
 lamps emitting radiation with a wavelength of between 500 and 700 nm and
 preferably 565 and 620 nm.
 The reaction is generally carried out at a temperature of between -20 and
 +40.degree. C. and preferably +10 and +20.degree. C.
 The reaction is generally carried out with vigorous stirring, for example
 by means of one or more recirculation pumps.
 The concentration of cyclododecanone oxime in the reaction medium should
 not generally exceed 15% by weight during the photonitrosation.
 The irradiated reaction mixture is continuously withdrawn and it is
 extracted with a strong acid, preferably sulphuric acid having a
 concentration of greater than 80% by weight, at a temperature of between
 10 and 50.degree. C., preferably of the order of 20 to 25.degree. C.
 The cyclododecanone oxime thus formed is subsequently subjected to a
 Beckmann rearrangement stage in the presence of sulphuric acid in order to
 form lauryllactam.

The examples which follow make it possible to illustrate the invention.
 EXAMPLE 1
 a--Photonitrosation
 A solution of cyclododecane in chloroform (450 g/l; 1 l/h), anhydrous
 gaseous hydrochloric acid to saturation and nitrosyl chloride are
 continuously introduced into a two liter (working volume) reactor equipped
 with a sodium vapour lamp having a power of 400 watts and emitting a
 radiation maximum in the vicinity of 595 nm. The nitrosyl chloride flow
 rate is adjusted so that the concentration in the reactor is maintained at
 2 g/l of reaction medium. The water content in the reaction medium is 300
 ppm.
 The effluent gases emerging from the reactor are directed to a condenser
 (recovery of the solvent) and a sparger containing a sodium hydroxide
 solution (trapping of the hydrochloric acid).
 The medium is continuously withdrawn at the rate of approximately 1.1 l/h.
 Under stationary conditions, 0.63 mol/h or cyclododecanone oxime, 0.023
 mol/h or monochlorocyclododecane, 0.0105 mol/h of chlorocyclododecanone
 oxime and 0.001 mol/h of dichlorocyclododecane are formed.
 The number of moles of cyclododecane converted in one hour is 0.670.
 The molar selectivity for cyclododecanone oxime is 0.94, calculated on the
 basis of the cyclododecane which has reacted.
 Under these conditions, the hourly productivity of oxime is 1295 g/kW
 (optical pathlength of the lamp: 6.7 cm; energy efficiency=24%).
 b--Beckmann rearrangement
 The reaction medium withdrawn in stage a is treated with 98.5% sulphuric
 acid in order to extract the cyclododecanone oxime therefrom. After
 separation by settling, the recovered sulphuric solution comprises 36% by
 weight of the oxime.
 200 g of the abovementioned sulphuric oxime solution are introduced over
 one hour into 100 g of 98.5% sulphuric acid maintained, with stirring, at
 155.degree. C. The mixture is subsequently brought to 160.degree. C. for
 30 minutes.
 71.28 g of lauryllactam are recovered (molar yield: 99%).
 The overall molar yield (photonitrosation+rearrangement) is 93%.
 EXAMPLE 2 (COMATIVE)
 a--Photonitrosation
 The reaction is carried out under the conditions of Example 1, modified in
 that the solution of cyclododecane in chloroform comprises 2000 ppm of
 water. A portion of this water is kept in suspension in the solution by
 stirring in the device for mixing cyclododecane and chloroform situated
 upstream of the feed to the reactor.
 In the stationary phase, 0.62 mol/h of cyclododecanone oxime, 0.0226 mol/h
 of monochlorocyclododecane, 0.0103 mol/h of chlorocyclododecanone oxime
 and 0.00098 mol/h of dichlorocyclododecane are formed.
 The number of moles of cyclododecane converted in one hour is 0.667.
 The molar yield of oxime is 0.929.
 b--Beckmann rearrangement
 The reaction is carried out under the conditions of Example 1. The
 sulphuric solution obtained after the extraction comprises 35% by weight
 of the oxime.
 When the reaction is complete, 67.9 g of lauryllactam are recovered (molar
 yield: 97%).
 The overall molar yield is 90.1%.
 EXAMPLE 3 (COMATIVE)
 a--Photonitrosation
 The reaction is carried out under the conditions of Example 1, modified in
 that a 90% aqueous sulphuric acid solution is additionally introduced
 continuously into the reactor, so that the volume injected represents 10%
 of the total volume of the reaction medium.
 The reaction medium continuously withdrawn is separated by settling. 0.43
 mol/h of cyclododecanone oxime and 0.011 mol/h of chlorocyclododecanone
 oxime are recovered in the aqueous phase, and 0.016 mol/h of
 monochlorocyclododecane and 0.0005 mol/h of dichlorocyclododecane are
 recovered in the organic phase.
 The number of moles of cyclododecane converted in one hour is 0.495.
 The molar selectivity for cyclododecanone oxime is 0.875, calculated on the
 basis of the cyclododecane which has reacted.
 Under these conditions, the hourly productivity of oxime is 890 g/kW.
 b--Beckmann rearrangement
 The reaction is carried out under the conditions of Example 1. The
 sulphuric solution obtained after the extraction comprises 30% by weight
 of the oxime.
 On conclusion of the rearrangement, 68.4 g of lauryllactam are recovered
 (molar yield: 97%).
 The overall molar yield is 84.8%.