What is Chloroacetic Acid
Chloroacetic acid is a chloro-carboxylic acid synthesized in the laboratory and commonly referred to as a mono-chloroacetic acid (MCA) or Chloroethanoic acid or 2-Chloroacetic acid. Chloroacetic acid carries a 2-chloro substituent. It functions as an alkylating agent and a herbicide. Hence, it functions not only as a chloro-carboxylic acid but also as a haloacetic acid. It’s derived from acetic acid and is a conjugate of a chloroacetate.
Felix LeBlanc first prepared chloroacetic acid or Chloroethanoic acid, French Chemist in the year 1843 by chlorinating acetic acid (CH3COOH) in the presence of sunlight. In 1857, Charles-Adolphe Wurtz, a French Chemist, also prepared Chloroacetic acid by reacting chloroacetyl chloride with water. In the same year, Reinhold Hoffmann, a German Chemist prepared Chloroethanoic acid by refluxing glacial acetic acid in the presence of sunlight and chlorine.
Structure of Chloroacetic Acid
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Molecular Structure of Chloroacetic Acid
Chloroacetic acid is a light-brownish or colourless crystalline solid that sinks or dissolves easily in water. The chloroacetic acid formula is C2H3ClO2, and the molar mass is 94.49 g·mol−1. The Chloroethanoic acid is a combustible and corrosive compound that becomes toxic when ingested, absorbed, inhaled, or penetrated through the skin barrier. The chloro-carboxylic acid causes thermal when transported in its molten state.
Properties of Chloroacetic Acid
Here, are a few physical and chemical properties of the Chloroacetic Acid-
Physical Properties
Chloroacetic acid is a colourless or light-brownish coloured, crystalline, and hygroscopic solid.
Chloroethanoic acid presents high solubility in water and has relatively good solubility in solutions like diethyl ether, methanol, acetone, or ethanol. However, it is sparingly soluble in chlorinated hydrocarbons and hydrocarbons solutions.
Chloroacetic acid molar mass is 94.49 g/mol, and density is 1.58 g/cm3.
Chloroacetic acid forms azeotropes with several organic compounds.
The boiling point of Chloroacetic acid is 189.3 °C, while the melting point of Chloroacetic acid is 63 °C.
Chemical Properties
Chloroacetic acid is a common synthetic organic intermediate, either as the acid itself or as an acid derivative.
Chloroethanoic acid reacts with inorganic oxides, bases, and carbonates or with organic bases to give salts. Sodium chloroacetate is an important commercial product produced.
Chloroacetic acid esters are obtained by reaction with alcohols or olefins, which are also industrially important.
Chloroacetyl chloride is a product from the acid reaction with POCl3, PCl3, PCl5, thionyl chloride (SOCl2), phosgene (COCl2), etc.
Why Is Chloroacetic Acid Stronger Than Acetic Acid?
Chloroacetic acid is stronger than acetic acid because- the presence of chlorine. The −Cl ion is an electron-withdrawing group that pulls the negative charge towards itself, causing an inductive effect.
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Inductive effect experienced by chloroacetic acid
This effect leads to the negatively charged density on the oxygen atom to reduce, hence stabilizing the conjugate base of chloroacetic acid.
In chloroacetic acid, the strongly electron-withdrawing or electron affinity chlorine gets instantly replaced by a hydrogen atom and becomes 100 times stronger as an acid rather than an acetic acid, and the nitroacetic acid formed becomes stronger than the latter.
Chloroacetic Acid Uses
Chloroacetic acid is manufactured in several hundred thousand tons as carboxymethyl cellulose CMC, commonly known as Cellulose Ethers.
The primary application of chloroethanoic acid is the production of herbicides based on aryl hydroxy acetic acids, commonly known as Chloro Phenoxy Alkanoic Acids. These herbicides have a broad spectrum of usage.
Methyl chloroacetate and Chloroacetic acid are an essential constituent employed for the preparation of insecticide- dimethoate and herbicides- benazoline and methyl b-naphthyl acetate.
Another important outlet for Chloroethanoic acid is the manufacture of thioglycolic acid prepared in large amounts and employed to produce stabilizers for polyvinyl chloride or PVCs. Another practical use of thioglycolic acid is in hair cosmetics for hair preparations.
Another significant importance of chloroacetic acid is in the production of N-lauryl betaine, a long-chain betaine, which is used as cleaning surfactants or in personal care products.
Health Hazards of Chloroacetic Acid
When inhaled or breathed in, chloroacetic acid can irritate the throat, lungs, and nose causing coughing, shortness of breath, and wheezing.
Chloroacetic acid is a corrosive chemical, and when it comes in contact with skin and eyes can cause severe irritation, burning sensation, and can even damage the eye.
High or repeated exposure to chloroacetic acid can affect kidneys.
High exposure to Chloroethanoic acid can cause blurred visions, muscle twitching, ‘pins and needles’, anxiety, restlessness, and hallucinations. However, excessive intake can lead to convulsions and even lead to death.
FAQs on Chloroacetic Acid
1. What is chloroacetic acid?
Chloroacetic acid, also known as monochloroacetic acid (MCA), is an organochlorine compound and a derivative of acetic acid. It is a carboxylic acid in which one of the hydrogen atoms of the methyl group has been replaced by a chlorine atom. It is a colourless, crystalline solid that is highly soluble in water and is an important building block in organic synthesis.
2. What is the chemical formula and structure of chloroacetic acid?
The chemical formula for chloroacetic acid is C₂H₃ClO₂ or, more descriptively, ClCH₂COOH. Its structure consists of a carboxyl group (-COOH) attached to a methyl group where one hydrogen is substituted by a chlorine atom. This chlorine atom is key to its chemical properties, particularly its acidity.
3. What are the main industrial uses of chloroacetic acid?
Chloroacetic acid is a crucial chemical intermediate with several major industrial applications. Key uses include:
- The production of carboxymethyl cellulose (CMC), a widely used thickener and stabiliser in food, pharmaceuticals, and detergents.
- Synthesis of herbicides, such as 2,4-D and MCPA, and insecticides like dimethoate.
- Manufacturing of thioglycolic acid, which is used in PVC stabilisers and hair care products (e.g., permanents and depilatories).
- Production of various pharmaceuticals, dyes, and other organic chemicals.
4. What are some key physical properties of chloroacetic acid?
Chloroacetic acid exhibits the following physical properties:
- Appearance: It is a colourless to light brown crystalline solid.
- Odour: It has a sharp, pungent odour.
- Solubility: It is highly soluble in water, as well as in common organic solvents like ethanol, ether, and benzene.
- Melting Point: It has a relatively high melting point, around 61-63°C, depending on its crystalline form.
5. What are the safety precautions for handling chloroacetic acid?
Handling chloroacetic acid requires strict safety measures as it is highly corrosive and toxic. Contact with skin or eyes can cause severe burns. Inhalation or ingestion can be fatal. Essential precautions include using personal protective equipment (PPE) such as chemical-resistant gloves, safety goggles, and a lab coat. It must be handled in a well-ventilated area, preferably within a fume hood, to avoid inhaling its vapours.
6. Why is chloroacetic acid a stronger acid than acetic acid?
Chloroacetic acid is significantly stronger than acetic acid due to the inductive effect (-I effect) of the chlorine atom. Chlorine is highly electronegative and withdraws electron density from the adjacent carbon atom. This effect is transmitted to the carboxyl group, making the O-H bond more polar and weaker. Consequently, the proton (H⁺) is released more easily, resulting in higher acidity.
7. How exactly does the inductive effect stabilise the conjugate base of chloroacetic acid?
When chloroacetic acid donates a proton, it forms the chloroacetate anion (ClCH₂COO⁻). The electron-withdrawing chlorine atom helps to disperse the negative charge of the anion. By pulling electron density towards itself, it reduces the charge concentration on the oxygen atoms of the carboxylate group. This delocalisation of charge makes the chloroacetate anion more stable than the acetate anion (from acetic acid), shifting the equilibrium towards dissociation and making chloroacetic acid a stronger acid.
8. How would the acidity change if chlorine was replaced by fluorine to make fluoroacetic acid?
If chlorine were replaced by fluorine, the resulting compound, fluoroacetic acid, would be an even stronger acid. This is because fluorine is the most electronegative element, exhibiting a more powerful electron-withdrawing inductive effect (-I effect) than chlorine. This stronger effect would further polarise the O-H bond and stabilise the resulting fluoroacetate anion more effectively, leading to a greater tendency to donate a proton and thus higher acidity.
9. What does the pKa value of chloroacetic acid (around 2.87) signify compared to acetic acid (4.75)?
The pKa value is a quantitative measure of acid strength; a lower pKa indicates a stronger acid. The pKa of chloroacetic acid (≈2.87) is nearly 2 units lower than that of acetic acid (≈4.75). Since the pKa scale is logarithmic, this means chloroacetic acid is almost 100 times more acidic than acetic acid. This significant difference highlights the powerful impact of the chlorine atom's inductive effect on the molecule's ability to dissociate in water.
10. How is chloroacetic acid typically prepared?
There are two primary methods for preparing chloroacetic acid. In the laboratory, it is often synthesized via the Hell-Volhard-Zelinsky (HVZ) reaction, where acetic acid is treated with chlorine in the presence of a catalyst like red phosphorus. Industrially, the most common method is the direct chlorination of acetic acid at elevated temperatures, often using a catalyst like acetic anhydride or acetyl chloride.
