HOMOPHTHALIC ANHYDRIDE

IUPAC Name: 4H-isochromene-1,3-dione 
Following is the structure of 1H-2-Benzopyran-1,3(4H)-dione (CAS NO.703-59-3):
                            
Empirical Formula: C₉H₆O₃
Molecular Weight: 162.1421 g/mol
Index of Refraction: 1.584
Molar Refractivity: 40.29 cm³
Molar Volume: 120.3 cm³
Density: 1.347 g/cm³
Flash Point: 159 °C
Sensitive: Moisture Sensitive
Surface Tension: 52 dyne/cm
Melting point: 140-142 °C(lit.)
Storage temp.: Refrigerator (+4°C)
Enthalpy of Vaporization: 56.66 kJ/mol
Boiling Point: 324.5 °C at 760 mmHg
Vapour Pressure of 1H-2-Benzopyran-1,3(4H)-dione (CAS NO.703-59-3): 0.000244 mmHg at 25 °C
Appearance of 1H-2-Benzopyran-1,3(4H)-dione (CAS NO.703-59-3): slightly yellow to beige or light green powder
Canonical SMILES: C1C2=CC=CC=C2C(=O)OC1=O
InChI: InChI=1S/C9H6O3/c10-8-5-6-3-1-2-4-7(6)9(11)12-8/h1-4H,5H2
InChIKey: AKHSBAVQPIRVAG-UHFFFAOYSA-N

1H-2-Benzopyran-1,3(4H)-dione (CAS NO.703-59-3) hasn't been listed as a carcinogen by ACGIH, IARC, NTP, or CA Prop 65. And the toxicological properties have not been fully investigated.

Hazard Codes: Xi
Risk Statements: 36/37/38 
R36/37/38:Irritating to eyes, respiratory system and skin.
Safety Statements: 26-36 
S26: In case of contact with eyes, rinse immediately with plenty of water and seek medical advice. 
S36:Wear suitable protective clothing.
WGK Germany: 3
F: 10-21

 1H-2-Benzopyran-1,3(4H)-dione , its cas register number is 703-59-3. It also can be called  Homophthalic anhydride ; and Benzoglutaric anhydride .
 1H-2-Benzopyran-1,3(4H)-dione (CAS NO.703-59-3) is hazardous, so the first aid measures and others should be known. Such as: When on the skin: first, should flush skin with plenty of water immediately for at least 15 minutes while removing contaminated clothing. Secondly, get medical aid. Or in the eyes: Flush eyes with plenty of water for at least 15 minutes, occasionally lifting the upper and lower eyelids. Then get medical aid soon. While, it's inhaled: Remove from exposure and move to fresh air immediately. Give artificial respiration while not breathing. When breathing is difficult, give oxygen. And as soon as to get medical aid. Then you have the ingesting of the product : Wash mouth out with water, and get medical aid immediately.
 1H-2-Benzopyran-1,3(4H)-dione (CAS NO.703-59-3) is moisture sensitive. It should avoid the condition like incompatible materials, exposure to moist air or water. It is not compatible with strong oxidizing agents, strong bases. And also prevent it to broken down into hazardous decomposition products: carbon monoxide, carbon dioxide. However, its hazardous polymerization will not occur. In addition, it should keep refrigerated. (Store below 4°C/39°F.) And it should be stored in a tightly closed container, or stored in a dry area. And it should be kept under a nitrogen blanket.