MTHP : A versatile solvent for greener reactions and processes
Yuusuke Saitou of Kuraray introduces MTHP and explains how it can contribute to Green Chemistry
In order to achieve the UN ’ s Sustainable Development Goals ( SDGs ), the chemical industry has been required over the past few years to develop the field of ‘ Green Chemistry . This is defined as reactions and synthetic processes that make it possible to reduce the amount of waste , CO 2 emissions and the industry ’ s environmental footprint .
Among the important factors in the achievement of Green Chemistry are catalysts , reagents used in the synthesis process and reaction equipment . Improvements and innovations related to these are at the heart of many projects , with solvents being one of the top concerns .
Solvents are used in large quantities for reactions and extractions . To make operations greener , solvent must be selected based on their safety , recyclability , waste reduction and wastewater load reduction . Kuraray supplies a novel solvent that satisfies many of these principles : 4-methyltetrahydropyran ( MTHP , Figure 1 ). In doing so , it addresses five of the ‘ 12 Principles of Green Chemistry ’: 1 . Prevention 2 . Safer chemical synthesis 5 . Use of safer solvents and auxiliaries 6 . Energy efficiency 12 . Accident prevention
Issues of conventional solvents
A solvent is chosen depending on whether its solubility can be applicable to the reaction or extraction operation in which it is to be used . The most commonly used solvents include halogenated solvents , such as chloroform and dichloromethane , toluene and tetrahydrofuran ( THF ) ( Figure 1 ).
Unfortunately , halogenated solvents and toluene are problematic due to their high toxicity . THF is widely used because of its high solubility , but its low oxidation stability and the formation of explosive peroxides makes it unsafe and difficult to recycle .
Moreover as THF is fully miscible with water , another solvent , such as ethyl acetate , is required in the extraction step after the reaction .
MTHP
THF
2MTHF
Diethyl ether
14- ' Dioxane
B . P .
[ O C ]
105
65
80
35
101
M . P .
[ O C ]
- 92
-109
-136
-116
12
D (
ensity Viscosity F . P .
20 ° c ) [ cP ]
[ ° C ]
0.86 0.78 6.5
0.89 0.55
-15
0.85 0.60 -11
0.70 0.24
-45
1.04 1.30 11
A considerable amount of THF elutes into the aqueous layer during the extraction process , which is problematic regarding recyclability and wastewater load .
Advantages of MTHP
Figure 2 shows the physical properties of MTHP and common ether solvents . The most important characteristic of MTHP is that it is highly hydrophobic even though its structure is similar to that of THF . The solubility of MTHP in water is 1.5 wt % and that of water in MTHP is 1.4 wt %, so they separate into two layers .
Because of these characteristics , MTHP offers the advantages of energy saving , reduced CO 2 emissions , and reduced wastewater load in work-up processes compared to when using THF . Figure 3 shows the
Solubility in water
[ wt %]
1.5
00
14
6.5
00
Solubility in solvent
[ wt %]
1.4
00
4.4
1.2
00
Azeotropic point [ O C ]
( H 2 O ratio )
85 ( 19wt %)
64 ( 6.0wt %)
71 ( llwt %)
34
( 1.3wt %)
88 ( 18wt %)
SP value *
[( cal / cm 3 )
AQ . 5 ]
9.0
9.5
8.9
7.6
10.0
Figure 1 – Structures of MTHP & other solvents
* Calculated according to " Hansen solubility parameters a user ' s handbook 2 nd edition , CRC Press , ISBN : 0-8493-7248-8 "
Figure 2 - Physical properties of MTHP & common ether solvents
H H u
I c1 ,,, 9 ' c1 H / 9 ' cl Cl Cl
I
6
4-methyltetrahydropyran ( MTHP )
Chloroform Dichloromethane
Toluene
( THFP )
30 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981