Synthesis of MTHPA (MHHPA) from maleic anhydride and pentadiene

 

Hydro-phthalic anhydrides -- tetra-hydrophthalic anhydride, hexa-hydrophthalic anhydride, methyl tetrahydrophthalic anhydride (MTHPA), and methyl hexahydrophthalic anhydride (MHHPA) -- are used by the electronic information industry and are important intermediates for the pharmaceutical, pesticide, resin, and national defense industries. They have low toxicity and low volatility and are mainly used for curing agents of epoxy resin.

 

The synthesis of MTHPA from maleic anhydride and pentadiene is a typical Diels-Alder condensation reaction, i.e. the unsaturated maleic anhydride with olefinic bonds is a dienophile. It takes a 1,4 addition reaction with pentadiene, a catenary diene with conjugated diene, to generate a cyclohexene ring - hydroaromatic compound. The production flow goes as followings: with polymerization inhibitors, maleic anhydride reacts with pentadiene to generate MTHPA; after a preliminary separation of MTHPA, isomerization catalyst is added to continue the reaction to generate liquid MTHPA; after rectification, the colorless, transparent liquid MTHPA presults. MHHPA is the product of the hydrogenation of MTHPAT and follows a similar process.

Product quality

Quality indicators of MTHPA

Item	Indicator
Appearance	Colorless, transparent liquid
Chroma (Pt-Co scale)	<200
Specific gravity (25℃)	1.21±0.04
Viscosity cp (25℃)	50~70
Melting point ℃	≤-15
Acid value mgKOH/g	660~670
Anhydride content %	≥41
Heating loss %	<1
Free acid %	<1

Quality indicators of MHHPA

Item	Indicator
Appearance	Colorless, transparent liquid
Specific gravity (25℃)	1.16±0.04
Viscosity cp (25℃)	50~60
Melting point ℃	≤-15
Acid value mgKOH/g	≥660
Iodine value	<2
HHPA content %	≥99%
Free acid %	≤0.5

 

Technical indicators