Basic Information

1. English Name: Squaric acid
2. CAS Number: 2892-51-5
3. Molecular Formula: C4H2O4
4. Molecular Weight: 114.06
5. Synonyms: Squaric acid, Square acid, 3,4-Dihydroxy-3-cyclobutene-1,2-dione

Physical Properties

1. Appearance: White to beige granular crystals
2. Melting Point: >300 °C (literature value) or 293 °C (another literature value)
3. Boiling Point: 250.96 °C
4. Density: 1.82 g/cm³
5. Flash Point: 190 °C
6. Solubility: 20 g/L (30 ºC)
7. pKa: 1.5 (at 25℃)

Chemical Properties

1. Squaric acid exhibits strong acidity with highly symmetric dianions, contributing to its excellent stability.
2. It can be oxidized by bromine or potassium permanganate.
3. It does not react with phenylhydrazine but produces a deep purple color with an aqueous solution of ferric chloride.
4. Its properties resemble those of carboxylic acids, allowing it to form salts with bases and generate acyl chlorides, mixed anhydrides, esters, and amides.

Applications

1. Synthetic Materials: Used as an intermediate in the synthesis of organic photoconductors, liquid crystal display materials, laser writing recording materials, and electrostatic photographic photoreceptor materials.
2. Pharmaceutical Chemistry: In drug synthesis, squaric acid and its derivatives can be used to synthesize antihistamines, antiviral drugs, and antibacterials.
3. Dye Industry: Squaric acid dyes are important functional dyes widely used in electrostatic copying, solar cells, and optical recording materials.
4. Other Applications: It can also be used in the synthesis of plant growth regulators, herbicides, etc.