N-BromoSuccinimide (NBS) is a five membered cyclic dicarboxylimide compound with bromine substituent on the nitrogen atom, with the chemical formula C4H4BrNO2, CAS 128-08-5. The appearance is white to milky white crystalline solid or powder, with a slight smell of bromine. Slightly soluble in water and acetic acid, soluble in acetone, tetrahydrofuran, dimethylformamide, dimethyl sulfoxide. For methanol and acetone solvents, the solubility of NBS increases with temperature. It is a chemical raw material commonly used in industry, mainly used to regulate low-energy bromination reaction, and is a good bromination reagent, which can replace hydrogen atom at benzyl or allyl position. It can also be used as an oxidant for oxidation of alcohols to aldehydes and ketones, and for oxidation of aldehydes to acids.
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C4H4BrNO2 |
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177 |
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178 |
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m/z |
177 (100.0%), 179 (97.3%), 178 (4.3%), 180 (4.2%) |
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C, 26.99; H, 2.27; Br, 44.89; N, 7.87; O, 17.98 |
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It is a commonly used reagnt in organic reactions. In recent years, new research progress has been made in the application of NBS in various organic reactions The latest research achievements in its use as catalyst, oxidant, selective brominating agent and polymerization initiator in the reaction process were reviewed.
N-bromosuccinimide (NBS) reagets in organic reactions is the bromination of allyl hydrogen, benzyl hydrogen and carbonyl q - hydrogen, namely Wohl Ziesler reaction. With the deepening of research, it is gradually found that NBS can also be used well as catalyst, oxidant and many other aspects, which shows the great application value and potential of NBS reagnt.
1. NBS as catalyst:
The catalytic addition of organic amines and olefins to produce nitrogen-containing organic compounds is of great significance to basic research and is also very important to chemical production. However, traditional reaction catalysts are often difficult to synthesize, expensive, and harsh in use conditions. Sudalai and others use NBS as a catalyst, and use toluenesulfonamide and alcohols as nucleophilic reagnts to react with active styrene under mild conditions to obtain amino Alkoxy derivatives. The yields of these two kinds of reactions are very high, and 100% of them are Markov additions
2. NBS as oxidant:
Oxidation of secondary alcohols to ketones is a very important organic synthesis step. Sharma et al reported that
NBS oxidizes many secondary alcohols to ketones. The cobalt complex of acetylacetone was used as catalyst. The reaction conditions are mild and the yield is high, but this method is not suitable for the conversion of primary alcohols.
3. Green chemistry direction of NBS reaction:
Carbon tetrachloride is usually used as the solvent for the free radical bromination reaction of NBS, but carbon tetrachloride is known to have a great damage to the ozone layer, which restricts its application.
Therefore, it is necessary to explore the conditions of the bromination reaction of NBS and find a substitute for carbon tetrachloride. Among them, solvent-free solid phase reaction has been extensively studied.
5. Research progress of NBS on carbonyl ortho hydrogen substitution of ketones:
NBS is a very good carbonyl a - site bromination reaget, which is easy to operate and widely used In order to improve the reaction rate and yield, many corresponding catalytic systems have been developed.
4. Application of
Living polymerization is a very important method to prepare polymers with specific structure and narrow molecular weight distribution. Because the N - Br bond in NBS is very active, it is easy to break under heating to obtain active succinimide free radicals and inert bromine free radicals initiated by free radicals. Therefore, NBS may be used as a chain initiated transfer terminator for free radical polymerization Percec used NBS as initiator and TiCp2C12 as catalyst to carry out free radical polymerization of vinyl chloride.
6 Other reactions involving N-BromoSuccinimide (NBS):
Zoller et al. cited a route to convert benzyl alcohol to benzyl bromide under neutral conditions. This reaction was then combined with the solid phase reaction. Benzyl bromide would remain on the reaction resin, and the excess reactants and other products (DMSO and succinimide) could be washed off with anhydrous solvent.
The application of NBS in organic reaction is more and more extensive The development of new application fields, the research of reaction mechanism, and the use of efficient catalysts are the main development trends of the application of NBS in organic reactions.
N-BromoSuccinimide (NBS):
1. It is obtained by bromination of succinimide. Grind succinimide and put it into the reation pot, add crushed ice and sodium hydroxide solution, stir and dissolve. Add the mixture of bromine and carbon tetrachloride under the condition of vigorous stirring and cooling, and filter it quickly after stirring for 2 minutes. Fully wash with ice water until colorless, then wash with a small amount of ethanol, and dry to get the finished product.
2. Ammonium succinate is synthesized from succinic acid and ammonia, heated and dehydrated to produce succinimide, and then brominated and refined to obtain the finished product.
3. Succinimide is prepared by reacting with NaBrO2 in the presence of HBr.
NBS is crystalline with a faint bromine smell. Melting point 173-175℃ (slight decomposition). Solubility (g/100g solvent, 25℃): water 1.47; acetone 14.40; carbon tetrachloride 0.02; glacial acetic acid 3.10. NBS can be prepared by reacting an ice-cooled NaOH solution of succinimide with an equimolar amount of bromine. It is mainly used in organic synthesis and as an additive for rubber products. It is a special brominating agent for the laboratory preparation of allylic bromoolefins and a regent for identifying primary, secondary and tertiary alcohols.
N-bromosuccinimide (NBS) is a mild bromination reagnt, which is suitable for bromination reactions at the allylic and benzyl positions. It not only has mild reaction conditions and is easy to operate, but also has high reaction selectivity and few side reations. Allyl and benzyl hydrogen atoms are relatively active. Bromination reations are easy to occur under high temperature, light or the presence of free radical initiators. Peroxides or azo compounds are used as initiators, and the dosage is generally 5% to 10%. The reation temperature is generally high. For allylic bromination, low temperature is conducive to the addition reation of olefinic bonds; for benzylic bromination, too high a reation temperature will increase the formation of benzylic dibrominates. Therefore, it is crucial to choose a suitable reation temperature. Most of the reaction solvents are anhydrous non-polar inert solvents such as carbon tetrachloride, benzene, and petroleum ether to avoid terminating free radical reactions and other side reactions.
NBS can react with aromatic ethers (such as anisole, m-anisole, -naphthyl methyl ether, etc.) to bromine the benzene ring. Afterwards, benzene and toluene can also react with NBS to bromine the benzene ring using a small amount of Friedel-Crafts reaction catalysts, such as aluminum chloride, zinc chloride or iron, to obtain bromobenzene and p-bromotoluene, respectively. The bromination reaction of m-toluene methyl ether and 6-methyl- -naphthyl methyl ether with NBS respectively, the reation formula is:
The addition reaction of N-bromosuccinimide to olefins under acid catalysis is an important method for preparing -halohydrins. This method has high stereoselectivity, high yield, pure product, mild reation and convenient operation. The yield is 82%. The reation formula is as follows:
Dimethyl sulfoxide (DMSO) is a very effective solvent. The application of NBS to react with olefins in aqueous DMSO can obtain a high yield and highly stereoselective addition product with a yield of 92%. The reaction formula is:
NBS is a very good carbonyl -position bromination reagnt. The reation is easy to operate and widely used. In order to improve the reation rate and yield, many corresponding catalytic systems have been developed. Yang et al. used Mg(ClO4)2 to catalyze NBS for rapid bromination of 1,3-dicarbonyl compounds. The reation proceeds mildly in CH3CN or EtOAc. The reation has good stereoselectivity and can be very convenient for preparing -brominated 1,3-dicarbonyl compounds that are very important in organic synthesis.
The traditional application of N-bromosuccinimide reagnt in organic reations is the bromination of allylic hydrogen, benzylic hydrogen and carbonyl -hydrogen. With the deepening of research, it is gradually found that NBS can also have many applications in many aspects such as catalyst and oxidant.
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