Have you ever wondered how carboxylic acids can be converted to -halo carboxylic acids? Look no further as we delve into the Hell-Volhard-Zelinsky reaction, named after the chemists who discovered it.
This process involves the use of a phosphorous catalyst and halogen gas to achieve the desired transformation. In this article, we will discuss the history of the HVZ reaction, the chemists behind it and examples of the reaction.
The History of HVZ Reaction
The HVZ reaction was discovered by three chemists: von Hell, Jacob Volhard, and Nikolay Zelinsky. In 1881, von Hell first reported that bromine added to carboxylic acid in the presence of red phosphorus yielded a -bromo carboxylic acid product.
However, he could not explain how the reaction proceeded. It was not until 1891 that Jacob Volhard identified the phosphorus catalyst as the key factor in the reaction.
Later, in 1901, Nikolay Zelinsky found that chloroform could be used as a solvent instead of bromine.
The Chemists Behind HVZ Reaction
Johann Franz von Hell (1844-1926) was a German chemist who conducted research on carboxylic acids and esters. He discovered the HVZ reaction and was the first to observe the formation of a -bromo carboxylic acid by adding bromine to a carboxylic acid.
Jacob Volhard (1834-1910) was a German scientist who contributed immensely to organic and inorganic chemistry. He was the first to identify the key factor behind the HVZ reaction- the use of red phosphorus as a catalyst.
Nikolay Zelinsky (1861-1953) was a Russian chemist who was particularly interested in natural gas and petroleum refining. He researched the HVZ reaction and found that chloroform could be used instead of bromine, thus making the reaction more versatile.
Examples of HVZ Reaction
The HVZ reaction can be used to synthesize various compounds. Some examples are:
1.
Conversion of phenylacetic acid to 2-bromo-2-phenylacetic acid
Phenylacetic acid can be converted into 2-bromo-2-phenylacetic acid using PBr3 in the HVZ reaction. The -bromo carboxylic acid is an important intermediate in the synthesis of many biologically active compounds.
2. Preparation of alanine through ammonolysis of 2-bromopropanoic acid
2-Bromopropanoic acid can be converted into alanine through ammonolysis in the presence of a catalyst.
This is an important reaction in the production of -amino acids which are constituents of proteins.
Conclusion
The Hell-Volhard-Zelinsky reaction is a versatile method for the synthesis of -halo carboxylic acids. It was first discovered by Johann Franz von Hell, and later identified by Jacob Volhard as a reaction that used red phosphorus as a catalyst.
Nikolay Zelinsky found that chloroform could be used as a solvent. The HVZ reaction has been used in the synthesis of various compounds, including the conversion of phenylacetic acid to 2-bromo-2-phenylacetic acid and the preparation of alanine through ammonolysis of 2-bromopropanoic acid.
The Hell-Volhard-Zelinsky (HVZ) reaction is a reaction used to convert carboxylic acids to their corresponding -halo carboxylic acid. This reaction is a nucleophilic substitution reaction, which involves three main steps: formation of a phosphorus intermediate, tautomerization, and hydrolysis.
Step 1: Formation of Phosphorus Intermediate
The first step of the HVZ reaction involves the reaction of a carboxylic acid with a phosphorus trihalide (PX3), where X is typically a halogen (i.e. Cl, Br, I). The carbonyl oxygen of the carboxylic acid forms a P-O bond, breaking one of the P-X bonds in the phosphorus trihalide.
This results in the formation of an intermediate with a phosphorus atom bonded to both an oxygen atom and a halide anion. The phosphorus intermediate is unstable and can rearrange through tautomerization.
Tautomerization is a process where a molecule switches between two isomers by moving a proton. In this case, the proton on the carbon adjacent to the carbonyl group is moved to the oxygen to form a -halo acyl halide intermediate.
Step 2: Tautomerization
In the tautomerization step, the -halo acyl halide intermediate rearranges to release hydrogen halide acid (HX) and a phosphine oxide. The phosphine oxide is a byproduct of the reaction and is not used further.
The -halo acyl halide is the key intermediate in the reaction, which is subsequently hydrolyzed to give the -halo carboxylic acid. Step 3: Hydrolysis
The final step of the HVZ reaction involves the hydrolysis of the -halo acyl halide intermediate to give the -halo carboxylic acid.
This is achieved by exposing the -halo acyl halide to water or an aqueous base. The hydrolysis involves a nucleophilic substitution reaction, where the halide anion is replaced by a hydroxyl ion (OH-) from water or an aqueous base.
The result is the formation of the desired -halo carboxylic acid. The mechanism of the HVZ reaction can be represented as:
Carboxylic acid + PX3 -> Phosphorus intermediate -> -halo acyl halide + HX + Phosphine Oxide
-halo acyl halide + H2O -> -halo carboxylic acid + HX
Examples of HVZ Reaction Mechanism
The HVZ reaction mechanism can be seen in the synthesis of 2-bromo-2-phenylacetic acid from phenylacetic acid. The reaction mechanism for this synthesis is as follows:
1.
Phenylacetic acid reacts with PBr3 to form a phosphorus intermediate. 2.
The phosphorus intermediate undergoes tautomerization to form 2-bromo-2-phenylacetyl bromide and phosphine oxide. 3.
The 2-bromo-2-phenylacetyl bromide undergoes hydrolysis to form 2-bromo-2-phenylacetic acid. Another example of the HVZ reaction mechanism is its role in the production of -amino acids.
2-Bromopropanoic acid can be converted into alanine through ammonolysis in the presence of a catalyst. This is an important reaction in the production of -amino acids which are constituents of proteins.
The reaction mechanism for this synthesis is as follows:
1. 2-Bromopropanoic acid reacts with NH3 to form an ammonium salt.
2. The ammonium salt undergoes nucleophilic substitution with Bromide to form a -halo acyl halide intermediate.
3. The -halo acyl halide intermediate reacts with water to form the desired -amino acid.
Conclusion
In conclusion, the Hell-Volhard-Zelinsky reaction is a nucleophilic substitution reaction that involves the use of a phosphorus trihalide, a carboxylic acid, and water or an aqueous base. The reaction proceeds through the formation of a phosphorus intermediate, tautomerization of the intermediate, and hydrolysis of the -halo acyl halide to form the desired -halo carboxylic acid.
The HVZ reaction mechanism has been used to synthesize various compounds, including 2-bromo-2-phenylacetic acid and -amino acids, which are important in the production of proteins. In summary, the Hell-Volhard-Zelinsky (HVZ) reaction is a significant method for converting carboxylic acids to -halo carboxylic acids.
The reaction involves three main steps: the formation of a phosphorus intermediate, tautomerization, and hydrolysis. The HVZ reaction mechanism has been used to synthesize various compounds, including 2-bromo-2-phenylacetic acid and -amino acids.
The importance of the HVZ reaction lies in its versatility and usefulness in the production of biologically active compounds and the study of protein synthesis. Remember that this reaction requires safety precautions before being carried out as it involves the use of halogen gas.
FAQs:
Q: How does the HVZ reaction work? A: The HVZ reaction converts carboxylic acids to their corresponding -halo carboxylic acids through the use of a phosphorus trihalide, water or an aqueous base, and a tautomerization process.
Q: What is the significance of the HVZ reaction? A: The HVZ reaction is significant for its versatility and usefulness in the production of biologically active compounds and the study of protein synthesis.
Q: What are some examples of the HVZ reaction? A: Some examples of the HVZ reaction include the conversion of phenylacetic acid to 2-bromo-2-phenylacetic acid and the preparation of alanine through ammonolysis of 2-bromopropanoic acid.
Q: What safety precautions should be taken before performing the HVZ reaction? A: Safety precautions such as proper handling of halogen gases should be taken before performing the HVZ reaction.