A New Process For Synthesizing Indigo Intermediate Isatin In Food Coloring

Indigo is a kind of very important blue edible pigment.It was originally extracted from a plant called bluegrass for dying fabrics.Due to the presence of indigo in fabrics excavated in many archaeological sites,indigo is considered to be the oldest dye in the world.Indigo is one of the colorants in food additives and is now widely used in the food,dying,and pharmaceutical industries.Isatin is an intermediate for the synthesis of indigo.In 1883,Baeyer was patented for the synthesis of isatin with o-nitrobenzaldehyde.Since then,the method of synthesizing indigo by using isatin as a raw material has gradually replaced the method of extraction from plants and has become the main source of indigo.This article mainly studied two methods of synthesizing indigo intermediate isatin,and obtained a milder reaction condition by improving its process.The main research content and related conclusions are as follows:First,Based on the synthesis of isatin by Sandmeyer method,the experimental conditions for the first step synthesis of isonitrosoacetanilide were studied.We used hydroxylamine sulfate instead of hydroxylamine hydrochloride to reduce the corrosive effect of the reaction solution on the reaction vessel in industrial production.In this experiment,the author found the best reaction conditions through single-factor experiments and orthogonal experiments: n(aniline): n(hydroxylamine sulfate)=1:1.4,n(aniline):n(anhydrous sodium sulfate)=1:6,reaction temperature 85?,the yield reached 97.68%,and the synthesis product was subjected to high-performance liquid chromatography and infrared The analysis was confirmed.Second,The reaction conditions were optimized based on the Sandmeyer method for the synthesis of isatin.The reaction temperature was controlled by adding low-boiling reagent A during the reaction.In this experiment,the author investigated the effect of different reagents A,concentrated the sulfuric acid concentration and reaction time on the reaction yield,and then found the optimal reaction conditions through orthogonal experiments: Reagent A was selected from dichloromethane,the concentration of concentrated sulfuric acid was 90%,and the reaction time was 2 hours,at this time,the target compound the yield rate was up to 91.47%,and the product was confirmed to be isatin by HPLC and IR characterization.Third,Based on the indigo-synthetic isatin method proposed in the literature,the experimental conditions for the reaction were optimized.First,single factor experiments were conducted to investigate the effect of the molar ratio of indigo and sodium bichromate,the concentration of the sulfuric acid solution and the reaction temperature on the reaction yield.Then based on the results of single-factor experiments,the optimal reaction conditions were found through orthogonal experiments: n(Indigo):n(sodium dichromate)=1:2,the concentration of the sulfuric acid solution was 70%,and the reaction temperature was 65?.Using the best synthesis conditions for confirmatory experiments,the yield of isatin was increased from 77% to 80.47%.The product was confirmed to be isatin by HPLC and IR characterization.This experiment provides a highly efficient theoretical basis for the industrial production of isatin.