Empirical Formula: C₈H₉ClOS
Molecular Weight: 188.6745
Nominal Mass: 188 Da
Average Mass: 188.6745 Da
Monoisotopic Mass: 188.006263 Da 
EINECS: 256-076-2 
Index of Refraction: 1.542
Molar Refractivity: 48.78 cm³
Molar Volume: 154.8 cm³
Surface Tension: 41.7 dyne/cm
Density: 1.218 g/cm³
Flash Point: 143.5 °C
Enthalpy of Vaporization: 55.47 kJ/mol
Boiling Point: 313.6 °C at 760 mmHg
Vapour Pressure: 0.000492 mmHg at 25 °C
Storage tempreture: 0-6 °C
Appearance: Clear gold to dark coloured liquid
Structure of 4-Chloro-1-(2-thienyl)butan-1-one (CAS NO.37439-34-2):
                      

 4-Chloro-1-(2-thienyl)butan-1-one (CAS NO.37439-34-2) 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.

 4-Chloro-1-(2-thienyl)butan-1-one , its cas register number is 37439-34-2. It also can be called 4-Chloro-2'-butyrothienone ; and 4-Chlorobutyrothiophene . It 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. Then you have the ingesting of the product: If victim is conscious and alert, give 2-4 cupfuls of milk or water. Get medical aid immediately.
In addition, 4-Chloro-1-(2-thienyl)butan-1-one (CAS NO.37439-34-2) could be stable under normal temperatures and pressures. It is not compatible with Strong oxidants.. And also prevent it to broken down into hazardous decomposition products: Irritating and toxic fumes and gases.