NL2017341B1 - Preparation of TMTHF - Google Patents

Abstract

The invention relates to a process for the preparation of 2,2,5,5-tetramethyltetrahydrofuran (TMTHF) comprising contacting a TMTHF precursor with a solid catalyst in the presence of water, wherein the TMTHF precursor is chosen from the group consisting of 2,5-dimethyl-1,5-hexadiene (DMH-1), and 2,5-dimethyl-2,4-hexadiene (DMH-2) and/or combinations thereof, and wherein the solid catalyst is a beta zeolite. It also relates to the use of a betazeolite catalyst for this process. It also relates to the use of the TMTHF prepared by the process of the invention as solvent.

Description

Title: Preparation of TMTHF Technical Field

The current invention relates to a process for the preparation of TMTHF, the use of a beta zeolite catalyst for the preparation of TMTHF, and the use of TMTHF as solvent, e.g., in a process for the polymerization of vinyl monomers.

Background Art

Pressure is mounting in the EU to move away from many of the most popular solvents currently in use. Some are facing bans due to their toxicity, such as NMP, dichloromethane and toluene. Additionally, owing to recent international agreements to fight climate change, chemical companies are required to reduce CO2 emissions for which solvents are a major contributor. This is due to the volumes in which they are used (up to 50% of the total mass of chemicals in the manufacture of active pharmaceutical ingredients), on top of the fact that they are sourced from petroleum and incinerated at the end of their lifetimes. In this way, carbon which has been stored in the earth’s crust for millions of years as oil is converted to CO2 and released to the atmosphere.

As biomass consumes CO2 to grow, the use of solvents which have been sourced from biomass leads to no net increase in the levels of atmospheric CO2, establishing a closed carbon cycle. In recent years, many bio-based solvents with diverse chemical, physical and solubility properties have been developed such as bio-ethanol, 2-methyltetrahydrofuran (2-MeTHF), dihydrolevoglucosenone (Cyrene), para-cymene and some ionic liquids. However, bio-based low polarity, low boiling solvents which can potentially replace traditional hydrocarbon solvents such as toluene and hexane, are underrepresented (see Sherwood et al. in Green Chem. 2016, 18, p3990). While 2-MeTHF is a viable option for some applications, it is an ether, and like most ethers, forms explosive peroxides due to their alpha-hydrogen atom. Hexamethyldisiloxane is another option, however its synthesis from biomass is not easy and upon combustion forms large quantities of ash.

This invention relates to the production of a non-peroxide-forming, low-boiling, low-polarity solvent that can potentially replace traditional hydrocarbon solvents such as toluene and hexane, and that can be produced from biomass (or in other words: is bio-based): 2,2,5,5-tetramethyltetrahydrofuran (TMTHF). TMTHF has a low boiling point of ~111 °C and low ETN value of 0.111, both comparable to toluene. Although TMTHF is an ether by definition as it contains an R-O-R’ group (where R and R’ are alkyl groups), it does not possess the peroxide-forming potential of other ethers such as THF or 2-MeTHF. This is due to the absence of a proton in the α-position relative to the ethereal oxygen. The α-proton in traditional ethers is readily removed by low energy light, forming radicals. Oxygen from the air can react with the radicals to form explosive peroxides. The rate of peroxide forming potential in ethers increases with increasing radical stability: primary α-carbon « secondary α-carbon < tertiary α-carbon. As TMTHF does not contain any α-protons due to it containing two quaternary ethereal carbons, the potential to form peroxides is removed. The combination of these very favourable properties make TMTHF a rare low-boiling, low-polarity molecule which does not possess peroxide-forming potential and can be easily produced from biomass.

Methods of producing TMTHF from a precursor molecule comprising contacting the precursor with a catalyst have been reported in literature. Especially catalytic methods with 2,5-dimethylhexane-2,5-diol as a precursor have been described. TMTHF synthesis routes using another precursor than 2,5-dimethylhexane-2,5-diol have rarely been published. In fact, only two publications seem to report on reactions with another precursor. In these two publications, Pogorhelski (in 1899, see Chem Zentralblatt. 70:773, and 1904, see Chem. Zentralblatt 75:578) reported on the production of TMTHF from dimethylhexadiene by the use of sulfuric acid in a sealed tube. However, no specifics of the reaction are available.

Apparently, TMTHF synthesis from 2,5-dimethylhexane-2,5-diol as a precursor is considered the only viable route. 2,5-dimethyl-2,5-hexanediol can be produced according to the method of US6956141 B1. This method makes use of fully petroleum derived building blocks. The current invention aims to provide a process for the preparation of TMTHF from a precursor which is obtainable via a wide variety of bio-based building blocks.

Summary of invention

Thereto, the current invention provides a process for the preparation of 2,2,5,5-tetramethyltetrahydrofuran (TMTHF) comprising contacting a TMTHF precursor with a solid catalyst in the presence of water, wherein the TMTHF precursor is chosen from the group consisting of 2,5-dimethyl-1,5-hexadiene (DMH-1), 2,5-dimethyl-2,4-hexadiene (DMH-2), 2,5-dimethyl-4-hexen-2-ol and combinations thereof, and wherein the solid catalyst is a beta zeolite.

Description of embodiments

The invention may be illustrated by the following reaction scheme:

2,5-dimethyl-1,5-hexadiene (DMH-1) and 2,5-dimethyl-2,4-hexadiene (DMH-2) are isomers. When contacted with a beta zeolite catalyst at a temperature of 85 - 200 °C in the presence of water, it is believed that 2,5-dimethyl-4-hexen-2-ol is produced as an intermediate before TMTHF is formed:

The intermediate product may therefore be used instead or in combination with DMH- 1 and/or DMH-2. Advantageously, DMH-1 and DMH-2 may be produced from bio-based building blocks. The inventors therefore found a new elegant way of producing TMTHF from bio-based building blocks.

Alternatively, the precursors may be made from petrochemical building blocks. DMH- 2 may for instance be made from 2,5-dimethyl-2,5-hexanediol, e.g., using a zeolite-molecular sieve catalyst as described in CN1171980, or by dehydration of 2,5-dimethyl-2,5-hexanediol with a montmorillonite clay catalyst as described in US4507518. DMH-2 may also be produced by by reacting at least one member selected from the group consisting of isobutylene and tertiary butanol with isobutyl aldehyde as described in US385688. A catalytic process for the synthesis of DMH-2 from 2,2,4- trimethyl-3 penten-1-ol has been described by R.G. Tonkyn “Synthesis of 2,5-dimethyl-2,4-hexadiene”, in Journal of Polymer Science Part A-1: Polymer Chemistry, Volume 7, Issue 6, June 1969, Pages 1569-1570. Other routes for producing the TMTHF precursors may be found in the prior art.

The process of the present invention makes use of zeolites. Zeolites are microporous crystalline silica-alumina composites. The presence of aluminium atoms in the framework results in an overall negative charge on the surface of the material. Metal counterions such as Ca2+ or Mg2+ are present in the pores and they can be exchanged with protons to produce an acidic surface. Zeolites are prepared using templating agents, the nature of which determines the size of the pores. Beta-zeolites are prepared using tetraethylammonium cations as the templating agent while ZSM-5 zeolites are prepared using tetrapropylammonium cations as the templating agent. Adjusting the Si/AI ratio effects the acidity of the material: higher Si/AI ratios reduce the number of active sites within the catalyst but increase the number of stronger acid sites and the surface hydrophobicity.

Zeolites are very cheap and are the most used catalysts in the petrochemical industry along with sulfuric acid. Zeolites are very robust, being able to take temperatures of over 1000 °C. Zeolites can be reactivated simply by calcination to remove organic material from the pores.

Preferably the beta zeolite catalyst has a Si/AI ratio of 150:1 or lower in respect of the amount of Si. More preferably, the beta zeolite catalyst has a Si/AI ratio of 30:1 or lower in respect of the amount of Si. Most preferably, the beta zeolite is beta-zeolite HBEA 25 and/or HCZB25.

It has been found that a combination of a liquid acid and a beta zeolite may also be used as catalyst. This may result in improved yield and/or conversion. Use of a combination is therefore preferred.

The TMTHF precursor, DMH-1 and/or DMH-2, may be in the liquid (melt or solution) or gas phase. For commercial scale production, contacting of the TMTHF precursor with a beta zeolite catalyst is preferably carried out in a flow reactor packed with the beta zeolite catalyst. In such a reactor, liquid and gas phase reactions using a solid state catalyst are easily performed. However, for smaller scale production, batch conditions will do.

Preferably the process is carried out at a temperature in the range of 85 - 200 °C. Higher yields and conversions may be obtained at increased temperatures. Accordingly the process is more preferably carried out at a temperature in the range of 100 - 175 °C. TMTHF, produced by the process of this invention, may suitably be used as solvent and in particular as environmentally friendly replacement for toluene.

The present invention will be explained in more detail by reference to the following Examples, but the invention should not be construed as being limited thereto.

Examples DMH-2 (5 mmol, 0.68 ml) and deionized water (50 mmol, 0.9 ml) were dissolved in a selection of 1,4-dioxane or diglyme (5 ml). These solutions were added to a 25 ml round-bottomed flask and heated to reflux temperature of respectively about 100°C or about 135°C. Upon reaching the desired temperature, 100 mg solid acid catalyst was added along with 10 mol% liquid acid catalyst and the mixture was stirred for 1.5 hours. As catalysts, liquid acids selected from trifluoroacetic acid, methyl sulfate, sulfuric acid or phosphoric acid were used. This was compared with a beta zeolite, HBEA 25.The yields and conversions were obtained by NMR and GC-FID of the organic phase. Results are summarized in table 1.

The experiments illustrate that the synthesis of TMTHF is not achieved using only a liquid acid as catalyst (comparative experiments 2 and 5). DMH-2 may be converted, but not into the desired product. Using a beta zeolite resulted in the conversion of DMH-2 with selectivity towards TMTHF. It is shown that the conversion and selectivity may be improved by using a liquid acid in combination with the beta-zeolite. This has yet to be optimized. It has also been shown that the conversion and selectivity may be improved by exercising the reaction at a higher temperature, in diglyme. Again, this reaction has not yet been optimized. A reaction in gas phase may be expected to result in further improvements. A scouting experiment in THF at reflux conditions (about 66°C) did not provide attractive results, indicating that elevated temperatures are indeed preferred.

Claims (9)

A process for the preparation of 2,2,5,5-tetramethyl tetrahydrofuran (TMTHF) comprising contacting a TMTHF precursor with a solid catalyst in the presence of water, the TMTHF precursor being selected from the group consisting of 2, 5-dimethyl-1,5-hexadiene (DMH-1), 2,5-dimethyl-2,4-hexadiene (DMH-2), 2,5-dimethyl-4-hexen-2-ol and combinations thereof, and wherein the solid catalyst is a beta zeolite. Process according to claim 1, wherein the solid catalyst has an Si / Al ratio of 150: 1 or lower with respect to the amount of Si, preferably 30: 1 or lower. The method according to claim 1 or 2, wherein the solid catalyst is HBEA 25 and / or HCZB 25. A method according to any of the preceding claims, wherein the contacting of TMTHF precursor with the solid catalyst is carried out continuously, for example in a power reactor packed with the solid catalyst, or in a batch reactor. A method according to any one of the preceding claims, which is carried out at a temperature in the range of 85 - 200 ° C. The method of claim 5, which is carried out at a temperature in the range of 100 - 175 ° C. The method of any one of the preceding claims, wherein the TMTHF precursor is biomass based. 8. Use of a beta zeolite catalyst for the preparation of TMTHF. Use of the TMTHF prepared by the process according to any of claims 1 to 7 as a solvent.