Fair Trade: Lanthanum chloride catalyzes hydrogen–chlorine exchange between chlorinated hydrocarbons

Jun 16, 2008

Because of its toxicity and the dangers involved in handling it, tetrachloromethane (carbon tetrachloride, CCl4) can no longer be used or produced in many countries. However, the processes used in the production of other chlorinated hydrocarbons, such as chloroform (trichloromethane, CHCl3), also produce CCl4 as a byproduct. What is the best way to get rid of this unwanted substance?

A team headed by Bert M. Weckhuysen at the University of Utrecht (Netherlands) has now found an interesting new approach that may lead to effective recycling. As the researchers report in the journal Angewandte Chemie, a lanthanum chloride catalyst induces CCl4 and its reaction partner dichloromethane (CH2Cl2) to exchange one chlorine atom for a hydrogen atom, forming nearly 100 % of the desired CHCl3.

In order to increase the catalyst surface, lanthanum chloride (LaCl3) was deposited onto carbon nanofiber supports. This results in a highly active, selective, and stable catalyst to facilitate the hydrogen–chlorine exchange between CCl4 and CH2Cl2.

“Computer calculations suggest,” says Weckhuysen, “that the mechanism occurs by way of two separate hydrogen–chlorine exchange reactions.”

It appears that the surface of the LaCl3 catalyst contains not only the terminal chlorine atoms of the crystal lattice, but also other weakly adsorbed species. CH2Cl2 swaps one of its hydrogen atoms for one such weakly bound chlorine atom. It leaves behind the hydrogen atom, which is in turn weakly adsorbed to the catalyst surface. This hydrogen atom can be taken up by CCl4, which in turn leaves one of its chlorine atoms behind on the catalyst surface. Both of these reaction steps produce chloroform exclusively; no byproducts come into play.

This new catalytic reaction is astonishing in that it was previously assumed that the presence of oxygen—either in the gas phase or bound to the crystal lattice of the catalyst—is required for such reactions. Says Weckhuysen: “We are reporting for the first time a lanthanum-based catalyst material that can activate both C-H and C-Cl bonds in the absence of oxygen.”

Citation: Bert M. Weckhuysen, Catalytic Hydrogen-Chlorine Exchange between Chlorinated Hydrocarbons under Oxygen-Free Conditions, Angewandte Chemie International Edition 2008, 47, No. 27, 5002–5004, doi: 10.1002/anie.200800270

Source: Angewandte Chemie

Explore further: Recycling industrial waste water: Scientists discover a new method of producing hydrogen

add to favorites email to friend print save as pdf

Related Stories

Solving mysterious enzyme structure

Dec 12, 2012

Scientists at the Max Planck Institute for Chemical Energy Conversion (MPI CEC) have solved a long-standing puzzle in photosynthesis research. With the aid of quantum chemistry they were able to provide unexpected ...

Developing the next generation of fuel cells

Mar 27, 2012

(PhysOrg.com) -- UConn’s Center for Clean Energy Engineering has developed a new manufacturing process for fuel cells that could make highly efficient, fuel cell-powered vehicles a viable commercial option ...

Recommended for you

A greener source of polyester—cork trees

10 hours ago

On the scale of earth-friendly materials, you'd be hard pressed to find two that are farther apart than polyester (not at all) and cork (very). In an unexpected twist, however, scientists are figuring out ...

Breakthrough points to new drugs from nature

11 hours ago

Researchers at Griffith University's Eskitis Institute have developed a new technique for discovering natural compounds which could form the basis of novel therapeutic drugs.

World's first successful visualisation of key coenzyme

12 hours ago

Japanese researchers have successfully developed the world's first imaging method for visualising the behaviour of nicotine-adenine dinucleotide derivative (NAD(P)H), a key coenzyme, inside cells. This feat ...

User comments : 0

More news stories

Breakthrough points to new drugs from nature

Researchers at Griffith University's Eskitis Institute have developed a new technique for discovering natural compounds which could form the basis of novel therapeutic drugs.

A greener source of polyester—cork trees

On the scale of earth-friendly materials, you'd be hard pressed to find two that are farther apart than polyester (not at all) and cork (very). In an unexpected twist, however, scientists are figuring out ...

Down's chromosome cause genome-wide disruption

The extra copy of Chromosome 21 that causes Down's syndrome throws a spanner into the workings of all the other chromosomes as well, said a study published Wednesday that surprised its authors.