10 Difference Between Protic And Aprotic Solvents (Protic Vs Aprotic)

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What Is Protic Solvent?

In chemistry, a protic solvent is a solvent that has a hydrogen atom bound to oxygen, nitrogen or a fluorine. Typically, any solvent that contains a labile His referred to as protic solvent. The molecules of such solvents readily donate protons to reagents.

Examples of Protic solvents are:

  • Water (H2O)
  • Alcohol (C2H5OH)
  • Formic acid (CH2O2)
  • Hydrogen fluoride (HF)
  • Ethanol (C2H5OH)
  • Methanol (CH3OH)
  • Ammonia (NH3)
  • Acetic acid (CH3COOH)

What You Need To Know About Protic Solvent

  1. Protic solvents are capable of hydrogen bonding because they contain at least one hydrogen atom connected directly to an electronegative atom (such as O-H or N-H bonds).
  2. Examples of Protic solvents are water, alcohol, formic acid, hydrogen fluoride, Ethanol, methanol, ammonia, acetic acid etc.
  3. Protic solvents display hydrogen bonding.
  4. Protic solvents have an acidic hydrogen (although they may be very weak acids such as ethanol).
  5. Polar protic solvents are often used to dissolve salts.
  6. SN1 reactions are significantly faster in polar Protic solvents than in polar Aprotic solvents.
  7. SN1 reaction works well for tertiary alkyl halide because the loss of the leaving group forms a tertiary carbonation which is the most stable form of carbocations. A polar protic solvent will stabilize this carbocation.
  8. Polar Protic solvents have high dielectric constants and high polarity.
  9. Polar Protic solvents are rich with O-H and N-H bonds.
  10. All protic solvents are prone to proton reduction to yield hydrogen gas and are only used for reductive electrochemistry.

What Is Aprotic Solvent?

An Aprotic solvent is a solvent molecule which contains no hydrogen atoms capable of acting as proton donor in hydrogen bonding interactions. These solvents generally have intermediate dielectric constants and polarity.

Examples of Aprotic solvents are:

  • Acetone
  • Dimethyl sulfoxide
  • DMF (N,N-dimethylformamide)
  • Acetonitrile
  • HMF (hydroxymethylfurfural)
  • Crown ethers

What You Need To Know About Aprotic Solvents

  1. Aprotic solvents contain no hydrogen atoms connected directly to an electronegative atom and they are not capable of hydrogen bonding.
  2. Examples of Aprotic solvents are acetone, dimethyl sulfoxide, DMF (N,N-dimethylformamide), acetonitrile, HMF (hydroxymethylfurfural), crown ethers etc.
  3. Aprotic solvents are solvents that can accept hydrogen bonds.
  4. Aprotic solvents do not have acidic hydrogen.
  5. Polar Aprotic solvents can dissolve salt. Their ability to dissolve salts depends strongly on the nature of the salt.
  6.  SN2 reactions are significantly faster in polar Aprotic solvents than in protic solvents.
  7. Polar Aprotic solvents work well for SN2 reactions because they do not solvate nucleophiles. For example, if we have potassium fluoride and crown ether as a solvent, this ether will solvate potassium, not fluoride. Then, the fluoride will be free to participate in the reaction with a substrate.
  8. Aprotic solvents generally have intermediate dielectric constants and high dipole moments.
  9. Aprotic solvents lack O-H and N-H bonds.
  10. Polar Aprotic solvents are generally incompatible with strong bases such as Grignard reagents or t-butyllithium. Aprotic solvents find applications in various industries such as oil and gas, paints and coatings, electronics and pharmaceuticals.

Also Read: Difference Between SN1 And SN2 Reaction

Difference Between Protic And Aprotic Solvents In Tabular Form

BASIS OF COMPARISON PROTIC APROTIC
Description Protic solvents are capable of hydrogen bonding because they contain at least one hydrogen atom connected directly to an electronegative atom (such as O-H or N-H bonds).   Aprotic solvents contain no hydrogen atoms connected directly to an electronegative atom and they are not capable of hydrogen bonding.  
Example Water, alcohol, formic acid, hydrogen fluoride, Ethanol, methanol, ammonia, acetic acid etc Acetone, dimethyl sulfoxide, DMF (N,N-dimethylformamide), acetonitrile, HMF (hydroxymethylfurfural), crown ethers
Hydrogen Bonding They display hydrogen bonding.   They display hydrogen bonding.  
Ability They are often used to dissolve salts.   They can dissolve salt. Their ability to dissolve salts depends strongly on the nature of the salt.  
Acidic Hydrogen They have acidic hydrogen (although they may be very weak acids such as ethanol).   They do not have acidic hydrogen.  
Effect On SN1 And SN2 SN1 reactions are significantly faster in polar Protic solvents than in polar Aprotic solvents.   SN2 reactions are significantly faster in polar Aprotic solvents than in protic solvents.  
Carbocation SN1 reaction works well for tertiary alkyl halide because the loss of the leaving group forms a tertiary carbonation which is the most stable form of carbocations. A polar protic solvent will stabilize this carbocation.   Polar Aprotic solvents work well for SN2 reactions because they do not solvate nucleophiles. For example, if we have potassium fluoride and crown ether as a solvent, this ether will solvate potassium, not fluoride. Then, the fluoride will be free to participate in the reaction with a substrate.  
Dielectric Constants & Polarity They have high dielectric constants and high polarity.   They generally have intermediate dielectric constants and high dipole moments.  
O-H &N-H Bonds They are rich with O-H and N-H bonds.   They lack O-H and N-H bonds.  
Application All protic solvents are prone to proton reduction to yield hydrogen gas and are only used for reductive electrochemistry.   Aprotic solvents find applications in various industries such as oil and gas, paints and coatings, electronics and pharmaceuticals.  

Also Read: Difference Between Cis And Trans Isomers

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