Empirical Formula: C₁₀H₁₀O₃
Molecular Weight: 178.1846
Nominal Mass: 178 Da
Average Mass: 178.1846 Da
Monoisotopic Mass: 178.062994 Da 
Index of Refraction: 1.591
Molar Refractivity: 50.38 cm³
Molar Volume: 149 cm³
Surface Tension: 46.2 dyne/cm
Density: 1.195 g/cm³
Flash Point: 132.6 °C
Enthalpy of Vaporization: 60.43 kJ/mol
Boiling Point: 329.9 °C at 760 mmHg
Vapour Pressure: 6.91E-05 mmHg at 25 °C
Melting point: 116-119 °C(lit.)
Appearance: White to light brown fine crystalline powder
Structure of 3-Methoxycinnamic acid (CAS NO.6099-04-3):
                        
IUPAC Name: (E)-3-(3-Methoxyphenyl)prop-2-enoic acid
Canonical SMILES: COC1=CC=CC(=C1)C=CC(=O)O
Isomeric SMILES: COC1=CC=CC(=C1)/C=C/C(=O)O
InChI: InChI=1S/C10H10O3/c1-13-9-4-2-3-8(7-9)5-6-10(11)12/h2-7H,1H3,(H,11,12)/b6-5+
InChIKey: LZPNXAULYJPXEH-AATRIKPKSA-N
Product Category of 3-Methoxycinnamic acid (CAS NO.6099-04-3): Aromatic Cinnamic Acids, Esters and Derivatives;Cinnamic acid;Acids & Esters;Anisoles, Alkyloxy Compounds & Phenylacetates

 3-Methoxycinnamic acid (CAS NO.6099-04-3) hasn't been listed as a carcinogen by NTP, IARC, ACGIH, or CA Prop 65.

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.

 3-Methoxycinnamic acid , its cas register number is 6099-04-3. It also can be called m-Methoxycinnamic acid ; trans-3-(3-Methoxyphenyl)acrylic acid ; and O-Methyl-m-cumaric acid . It is hazardous, so the first aid measures and others should be known. Such as: When on the skin: Flush skin with plenty of water for at least 15 minutes while removing contaminated clothing and shoes. Or in the eyes: Immediately flush eyes with plenty of water for at least 15 minutes, occasionally lifting the upper and lower eyelids. While, it's inhaled: Remove from exposure and move to fresh air immediately. Then you have the ingesting of the product: Do NOT induce vomiting. If conscious and alert, rinse mouth and drink 2-4 cupfuls of milk or water.
In addition, 3-Methoxycinnamic acid (CAS NO.6099-04-3) could be stable under normal temperatures and pressures. It is not compatible with strong oxidizing agents, and you must not take it with incompatible materials. And also prevent it to broken down into hazardous decomposition products: Carbon monoxide, irritating and toxic fumes and gases, carbon dioxide.