Preparation Of Organic Intermediates Containing Bromine Element

Organic compounds containing bromine element are widely used in medicine,pesticides and all kinds of industrial additives,and are also important intermediates in organic synthesis.Commonly used bromination reagents include bromine,N-bromosuccinimide（NBS）,1,3-dibromo-5,5-dimethylhydantoin（DBDMH）,etc.Because of the high toxicity and corrosion of bromine and the high cost of bromination reagents such as NBS and DBDMH,it is very important to develop a safe and economical process for the organic compounds containing bromine element.The preparation of 4-bromo-N,N-dimethylaniline,1,2-dibromoalkanes,1,2-dibromoalkenes,（1-bromoethyl）benzene,（1,1-dibromoethyl）benzene and（1,1,2-tribromoethyl）benzene were described in this paper.Firstly,the preparation of 4-bromo-N,N-dimethylaniline was investigated.With the mixture of ethyl acetate and water as solvent,the 4-bromo-N,N-dimethylaniline can be prepared by the reaction of N,N-dimethylaniline with bromine which was formed in situ via the REDOX reaction of Na Br,H₂O₂and excess acid.Under optimized conditions,the yield of 4-bromo-N,N-dimethylaniline reached 88%when the reaction was amplified to 1 mol（121 g）.This method has the advantages of simple operation,safety,high selectivity and good process stability.Secondly,the preparation of 1,2-dibromoalkanes（or 1,2-dibromoalkenes）were studied.In the presence of H₂SO₄,1,2-dibromoalkanes（or 1,2-dibromoalkenes）were obtained by the electrophilic addition recation of alkenes（or alkynes）with the bromine formed in situ via the REDOX reaction of NaBrand NaBrO₃.The reaction has good selectivity and wide application range.The amplification experiment of（E）-2,3-dibromo-2-butene-1,4-diol（1.2 mol,103 g）proved that the reproducibility of the process was good and the yield was stable,it shows that the process has a good industrialization prospect.Thirdly,the synthesis of（1-bromoethyl）benzene、（1,1-dibromoethyl）benzene and（1,1,2-tribromoethy）benzene were studied.In the presence of AIBN,the bromine generated in-situ by the reaction of NaBrO₃,NaBrand H₂SO₄can react with ethylbenzene.By controlling the dosage of NaBrO₃-Na Br-H₂SO₄,（1-bromoethyl）benzene,（1,1-dibromoethyl）benzene and（1,1,2-tribromoethyl）benzene can be selectively obtained.The brominated products can be eliminated by alkali to give vinylbenzene,ethynylbenzene and（2-bromoethynyl）benzene,respectively.Hydrolysis of（1,1-dibromoethyl）benzene and（1,1,2-tribromoethyl）benzene in 40%hydrobromic acid yields the corresponding acetophenone andα-bromoacetophenone.Using 3-nitroethylbenzene（0.9 mol,136.5 g）as raw material,the total yield of1-ethyny-3-nitrobenzene was 77%after bromination and elimination reaction.