DL-Mandelic acid

DL-Mandelic Acid

Chemical Name:
DL-2-Hydroxy-2-phenylacetic acid (IUPAC name). Also known as DL-amygdalic acid or racemic mandelic acid.

Structural Formula:
A chiral molecule with a benzene ring attached to a central carbon bearing both a hydroxyl (-OH) and a carboxylic acid (-COOH) group. The "DL" designation indicates a racemic mixture of equal parts D- and L-enantiomers.

Molecular Formula:
C₈H₈O₃

Physical Properties:

• Appearance: White crystalline powder.

• Melting Point: ~118–120°C (varies slightly with purity).

• Solubility:

  • Moderately soluble in water (enhanced by heating).

  • Freely soluble in polar solvents (e.g., ethanol, ether).

• Optical Activity: Optically inactive (racemic mixture cancels enantiomeric rotation).

Chemical Properties:

• Acidity: Weak organic acid (pKa ~3.4) due to the carboxylic acid group.

• Reactivity:

  • Undergoes esterification, oxidation, and decarboxylation.

  • Acts as an α-hydroxy acid (AHA), enabling exfoliation via keratin dissolution.

  • Chelates metal ions (e.g., copper, iron).

• Stability: Stable under dry conditions but hygroscopic; decomposes at high temperatures.

Synthesis:

1. Cyanohydrin Route:

   • Benzaldehyde reacts with hydrogen cyanide (HCN) to form mandelonitrile.

   • Hydrolysis of mandelonitrile (acidic or basic conditions) yields DL-mandelic acid.

2. Reduction of Phenylglyoxylic Acid:

   • Catalytic hydrogenation or chemical reduction of phenylglyoxylic acid (C₆H₅COCOOH).

Applications:

1. Skincare:

   • Exfoliation: Promotes cell turnover in acne, hyperpigmentation, and aging treatments.

   • Antimicrobial: Effective against acne-causing bacteria (e.g., Cutibacterium acnes).

2. Pharmaceuticals:

   • Urinary tract antiseptic (often as ammonium or sodium salts).

   • Intermediate in synthesizing antibiotics (e.g., mandelic acid derivatives).

3. Industrial:

   • Chiral resolving agent for enantiomer separation.

   • Precursor for fragrances and agrochemicals.