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Acetonitrile is a poisonous, colourless liquid with a sweet, burnt taste and an ether-like odour. Cyanomethane, ethyl nitrile, ethanenitrile, methane carbonitrile, acetonitrile cluster, and methyl cyanide are some of its other names. It is represented by a chemical formula C2H3N. It is primarily created as a byproduct of the acrylonitrile manufacturing process. It is employed in chemical synthesis and in butadiene purification as a polar aprotic solvent.
Read More: Class 12 Aldehydes, Ketones and Carboxylic
Key Terms: Acetonitrile, cynides, compounds, methane carbonitrile, Hydrogen, carbon, ether, solvent, Cyanomethane, ethyl nitrile, ethanenitrile, acetonitrile cluster, methyl cyanide
Acetonitrile and its Structure
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Acetonitrile is the simplest organic nitrile which is often abbreviated as MeCN. It is a toxic and colourless liquid with an ether-like odour. It is represented by a chemical formula C2H3N. The carbon atom of acetonitrile is triple bonded with the nitrogen atom.
Structure of Acetonitrile
The linear NC-C skeleton has a short CN distance of 1.16Å. Jean-Baptiste Dumas, a French scientist, created acetonitrile for the first time in 1847.
Read More: IUPAC Nomenclature of Organic Compounds
Physical Properties of Acetonitrile
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The various physical properties of acetonitrile are tabulated below.
| Parameters | Values |
|---|---|
| Molecular Weight | 41.05 |
| Boiling point | 81.60°C |
| Vapour pressure | 88.8 Torr at 25°C |
| Freezing point | -43.8°C |
| Refractive index | 1.3441 at 20°C |
| Density | 0.7822 g/mL (6.527 lb/gal) at 20°C 0.7766 g/ml (6.481 lb/gal) at 25°C |
| Dielectric constant | 37.5 at 20°C |
| Dipole moment | 3.44 D at 20°C |
| Solvent group | 3.44 D at 20°C |
| Surface tension | 19.10 dyn/cm at 20°C |
Also Read: Activation Energy Formula
Chemical Properties of Acetonitrile
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The following reactions of acetonitrile give us an idea of its chemical properties.
- Acetonitrile reaction with water
Heat, sparks, or flames can easily ignite acetonitrile, which produces very hazardous hydrogen cyanide gases when heated. It is easily dissolved in water. When it reacts with water, steam, or acids, it produces flammable vapours and when this is exposed to air, can generate explosive combinations.
Acetonitrile with water equilibrium graph
- Acetonitrile reaction with Hydrochloric Acid
Acetamide is generated when acetonitrile is partially hydrolyzed in cold concentrated HCl. It produces carboxylic acid after full hydrolysis.
Reaction with HCl
- Acetonitrile reaction with Sulphuric Acid
If acetonitrile is treated with dilute aqueous sulfuric acid, the most likely reaction is acid-catalyzed hydrolysis:
CH3C ≡ N + H2O → CH3COOH + NH3
(In acid, the ammonia would be protonated)
Also Read:
| Chemistry Related Articles | ||
|---|---|---|
| Transesterification | Electron Gain Enthalpy | Ester Hydrolysis |
| sn1 Reaction Mechanism | Electronegativity | VSEPR Theory |
Production of Acetonitrile
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Acetonitrile is mostly created as a byproduct of the Sohio process, which involves propylene ammoxidation. As a consequence of the aforementioned acrylonitrile synthesis process, hydrogen cyanide is generated. In a fluidised bed reactor, propylene, ammonia, and air are reacted to form ACN, with acetonitrile and hydrogen cyanide as by-products. Acetonitrile is made as a raw material.
Sohio Process
Advantages of Acetonitrile
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- Acetonitrile acts as a medium for acid-base investigations.
- It facilitates the dissociation of ion pairs into free ions due to its high relative permittivity (∈r=36).
- It is a good distinguishing solvent due to its low autoprotolysis constant (estimated pKauto around or greater than 406).
Acetonitrile used as a Solvent
- In terms of solvability, acetonitrile is a strongly polar solvent that is comparable to alcohols. Like alcohols, acetonitrile is a strong acceptor of hydrogen bonds rather than a donor of hydrogen bonds.
- Acetonitrile nitrogen is slightly basic, although it can be quite nucleophilic in this regard, akin to pyridine.
Also Read: Unsaturated Hydrocarbons, Saturated Hydrocarbons
Uses of Acetonitrile
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- As a Solvent: Acetonitrile is the most common solvent used by pharmaceutical companies. Acetonitrile is used to mould and cast plastic items, spin fibres, and extract fatty acids from vegetable oils and animals, as well as in lithium batteries.
- Acetonitrile is also required in chemical laboratories for the detection of a wide range of compounds, including pesticide residues.
Wide uses of Acetonitrile in labs
- Starting Ingredient: Many people use acetonitrile as a starting ingredient when making various compounds. Some of them are Acetomidine, Thiamine, acetic acid (alpha-naphthyl), Acetophenone.
- Distillation of Extracts: Acetonitrile is used in extractive distillation in the petrochemical sector. Because organic compounds and acetonitrile are selectively miscible, it is a popular choice for this market segment. C4-hydrocarbons and olefin-diolefin combinations are separated using it.
- Acetonitrile dissolves entirely in water and mixes with carbon tetrachloride, chloroform, acetone, ether, ethanol, and even ethylene chloride.
- Removing Solution: Acetonitrile can also be used to remove phenols, colouring materials, and tars from petroleum hydrocarbons. Acetonitrile and the other elements specified are insoluble.
Acetonitrile used in nail polish remover
- Solvent in laboratory: Acetonitrile is also extensively used in laboratories to crystallise a wide range of compounds. This chemical is also frequently used as a solvent in HPLC analysis.
- Other common uses of acetonitrile are in Pharmaceutical solvents, Perfume manufacture, Refining and extraction of copper, Recrystallizing steroids, reaction promoting medium and chlorinated solvents as stabilizers.
Health Hazards of Acetonitrile
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Acetonitrile can produce headaches, nausea, dizziness, agitation, disorientation, sleepiness, and palpitations when inhaled, ingested, or absorbed via the skin. Loss of consciousness and coma can occur in circumstances of acute poisoning, fits, and cardiac difficulties.
Toxicity
In small doses, acetonitrile has low toxicity. It can be broken down into hydrogen cyanide, which is the source of the deadly effects. The time it takes for the body to convert acetonitrile to cyanide is about 2–12 hours.
Human cases of acetonitrile poisoning (or, to be more specific, cyanide poisoning after exposure to acetonitrile) are uncommon but not unknown. Acetonitrile poisoning can occur through inhalation, ingestion, or (potentially) skin absorption. Breathing difficulties, a sluggish pulse rate, nausea, and vomiting are common symptoms.
Effects of Acetonitrile
In severe situations, convulsions and unconsciousness can occur, followed by death from respiratory failure. Oxygen, sodium nitrite, and sodium thiosulfate are among the most often used emergency therapies for cyanide poisoning.
Also Read: Electrophilic Aromatic Substitution
Things to Remember
- Acetonitrile is a poisonous, colourless liquid with a sweet, burnt taste and an ether-like odour.
- Cyanomethane, ethyl nitrile, ethanenitrile, methane carbonitrile, acetonitrile cluster, and methyl cyanide are some of the other names of acetonitrile.
- Acetonitrile is represented by the chemical formula C2H3N.
- Acetonitrile is the simplest organic nitrile which is often abbreviated as MeCN.
- When Acetonitrile reacts with water, steam, or acids, it produces flammable vapours and when this is exposed to air, can generate explosive combinations.
- Acetonitrile is mostly created as a byproduct of the Sohio process.
- Acetonitrile can produce headaches, nausea, dizziness, agitation, disorientation, sleepiness, and palpitations when inhaled, ingested, or absorbed via the skin.
- Acetonitrile is the most common solvent used by pharmaceutical companies.
Also Read:
Sample Questions
Ques 1. What is the purpose of using acetonitrile as a solvent in HPLC? (2 marks)
Ans. Because of its low UV cutoff, lesser viscosity (methanol creates very viscous mixes with water at certain concentrations), and greater boiling point, acetonitrile is frequently used.
Ques 2. What is the use of Acetonitrile? (2 marks)
Ans. Chemists utilise it as a solvent for chemical reactions and chromatography. Acetonitrile is used to extract fatty acids from vegetable oil. Perfumes are made with acetonitrile. Acetonitrile is commonly used in the manufacturing of synthetic medicines.
Ques 3. Suggest the most important type of intermolecular attractive interaction in the following pairs: (5 marks)
(i) n-hexane and n-octane
(ii) I2 and CCl4
(iii) NaCl04 and water
(iv) methanol and acetone
(v) acetonitrile (CH3CN) and acetone (C3H60)
Ans. (i) Both w-hexane and n-octane are non-polar. Thus, the intermolecular interactions will be London dispersion forces.
(ii) Both I2 and CCl4 are non-polar. Thus, the intermolecular interactions will be London dispersion forces.
(iii) NaCl04 is an ionic compound and gives Na+ and Cl04– ions in the Solution. Water is a polar molecule. Thus, the intermolecular interactions will be ion-dipole interactions.
(iv) Both methanol and acetone are polar molecules. Thus, intermolecular interactions will be dipole-dipole interactions.
(v) Both CH3CN and C3H6O are polar molecules. Thus, intermolecular interactions will be dipole-dipole interactions.
Ques 4. The depression in the freezing point of water observed for the same amount of acetic acid, trichloroacetic acid and trifluoroacetic acid increases in the order given above. Explain briefly. (2 marks)
Ans. Fluorine being more electronegative than chlorine has the highest electron-withdrawing inductive effect. Thus, trifluoroacetic acid is the strongest trichloroacetic acid is second-most and acetic acid is the weakest acid due to the absence of an electron-withdrawing group. Thus, CF3COOH ionizes to the largest extent while CH3COOH ionizes to a minimum extent in water. The greater the extent of ionization is the depression in the freezing point. Hence, the order of depression in the freezing point will be CH3COOH < CCl3COOH < CF3COOH.
Ques 5. Explain the significance of sodium, potassium, magnesium and calcium in biological fluids. (3 marks)
Ans. Sodium ions:
- Na+ ions participate in the transmission of nerve signals, in regulating the flow of water across cell membranes.
- In the transport of sugars and amino acids into cells.
Potassium ions:
- They activate many enzymes.
- Participate in the oxidation of glucose to produce ATP.
Magnesium ions:
- All enzymes that utilise ATP in phosphate transfer require magnesium as a cofactor.
- Mg is the main pigment for the absorption of light in plants.
Calcium:
- Ca2+ ions are present in bones.
- plays important roles in neuromuscular function.
Ques 6. State as to why
(a) a solution of Na2CO3 is alkaline?
(b) alkali metals are prepared by electrolysis of their fused chlorides?
(c) Sodium is found to be more useful than potassium? (3 marks)
Ans. (a) Na2CO3 is a salt of a weak acid, carbonic acid (H2CO3) and a strong base NaOH. Thus it undergoes hydrolysis to produce a strong base NaOH and its aqueous solution is alkaline in nature.
Na2CO3(s) + H2O(l)———–>2NaOH
(b) Because the discharge potential of alkali metals is much higher than that of hydrogen, therefore when the aqueous solution of an alkali metal chloride is subjected to electrolysis, H2, instead of the alkali metal, is produced at the cathode. Therefore alkali metals are prepared by electrolysis of their fused chlorides.
(c) Since potassium is more reactive than sodium and it is found in nature to a lesser extent than Na, sodium is found to be more useful.
Ques 7. Calculate the mass percentage of benzene (C6H6) and carbon tetrachloride (CCl4) if 22 g of benzene is dissolved in 122 g of carbon tetrachloride. (2 marks)
Ans. Mass of solution = Mass of C6H6 + Mass of CCl4
= 22 g+122 g= 144 g
Mass % of Benzene = 22/144 x 100 =15.28 %
Mass % of CCl4 = 122/144 x 100 = 84.72 %
Ques 8. Calculate the mass of urea (NH2CONH2) required in making 2.5 kg of 0.25 molal aqueous solution. (2 marks)
Ans. 0.25 Molal aqueous solution to urea means that
moles of urea = 0.25 mole
mass of solvent (NH2CONH2) = 60 g mol-1
.’. 0.25 mole of urea = 0.25 x 60=15g
Mass of solution = 1000+15 = 1015g = 1.015 kg
1.015 kg of urea solution contains 15g of urea
.’. 2.5 kg of solution contains urea =15/1.015 x 2.5 = 37 g
Ques 9. What are the effects of acetonitrile on health? (2 marks)
Ans. Acetonitrile can produce headaches, nausea, dizziness, agitation, disorientation, sleepiness, and palpitations when inhaled, ingested, or absorbed via the skin. Loss of consciousness and coma can occur in circumstances of acute poisoning, fits, and cardiac difficulties.
Ques 10. How is Acetonitrile produced? (2 marks)
Ans. Acetonitrile is mostly created as a byproduct of the Sohio process, which involves propylene ammoxidation. As a consequence of the aforementioned acrylonitrile synthesis process, hydrogen cyanide is generated. In a fluidised bed reactor, propylene, ammonia, and air are reacted to form ACN, with acetonitrile and hydrogen cyanide as by-products. Acetonitrile is made as a raw material.
Ques 11. What is the reaction of Acetonitrile with water? (2 marks)
Ans. Heat, sparks, or flames can easily ignite acetonitrile, which produces very hazardous hydrogen cyanide gases when heated. It is easily dissolved in water. When it reacts with water, steam, or acids, it produces flammable vapours and when this is exposed to air, can generate explosive combinations.
Ques 12. What are the advantages of Acetonitrile? (2 marks)
Ans.
- Acetonitrile acts as a medium for acid-base investigations.
- It facilitates the dissociation of ion pairs into free ions due to its high relative permittivity (∈r=36).
- It is a good distinguishing solvent due to its low autoprotolysis constant (estimated pKauto around or greater than 406).
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