The 3-Hydroxyphthalic anhydride, with the CAS registry number 37418-88-5, is also known as 4-Hydroxyisobenzofuran-1,3-dione. It belongs to the product categories of Phthalic Acids, Esters and Derivatives; Anhydride Monomers; Monomers; Polymer Science; Carbonyl Compounds; Carboxylic Acid Anhydrides; Organic Building Blocks. This chemical's molecular formula is C₈H₄O₄ and molecular weight is 164.11. What's more, its systematic name is 4-Hydroxy-2-benzofuran-1,3-dione. This chemical should be sealed and stored in a cool and dry place. It is used to modify proteins. 

Physical properties of 3-Hydroxyphthalic anhydride are: (1)ACD/LogP: 1.301; (2)# of Rule of 5 Violations: 0; (3)ACD/LogD (pH 5.5): 1.23; (4)ACD/LogD (pH 7.4): 0.13; (5)ACD/BCF (pH 5.5): 4.88; (6)ACD/BCF (pH 7.4): 1.00; (7)ACD/KOC (pH 5.5): 103.31; (8)ACD/KOC (pH 7.4): 8.16; (9)#H bond acceptors: 4; (10)#H bond donors: 1; (11)#Freely Rotating Bonds: 1; (12)Polar Surface Area: 63.6 Å²; (13)Index of Refraction: 1.666; (14)Molar Refractivity: 37.563 cm³; (15)Molar Volume: 100.993 cm³; (16)Polarizability: 14.891×10^-24cm³; (17)Surface Tension: 76.2 dyne/cm; (18)Density: 1.625 g/cm³; (19)Flash Point: 160.238 °C; (20)Enthalpy of Vaporization: 63.578 kJ/mol; (21)Boiling Point: 365.42 °C at 760 mmHg; (22)Vapour Pressure: 0 mmHg at 25°C.

Uses of 3-Hydroxyphthalic anhydride: it can be used to produce 3-ethoxy-phthalic acid by heating. It will need reagent 10 percent sodium hydroxide and solvent H₂O with the reaction time of 24 hours. The yield is about 65%.

When you are using this chemical, please be cautious about it as the following:
It is irritating to eyes, respiratory system and skin. In case of contact with eyes, you should rinse immediately with plenty of water and seek medical advice. When using it, you need wear suitable protective clothing.

You can still convert the following datas into molecular structure:
(1)SMILES: O=C1OC(=O)c2cccc(O)c12
(2)Std. InChI: InChI=1S/C8H4O4/c9-5-3-1-2-4-6(5)8(11)12-7(4)10/h1-3,9H
(3)Std. InChIKey: CCTOEAMRIIXGDJ-UHFFFAOYSA-N

The toxicity data is as follows: