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: Four billion-year-old chemistry in cells today

add to favorites email to friend print save as pdf

Related Stories

How Kindle Unlimited compares with Scribd, Oyster

2 hours ago

Amazon is the latest—and largest—company to offer unlimited e-books for a monthly fee. Here's how Kindle Unlimited, which Amazon announced Friday, compares with rivals Scribd and Oyster.

NASA sees powerful thunderstorms in Tropical Storm Matmo

3 hours ago

Strong thunderstorms reaching toward the top of the troposphere circled Tropical Storm Matmo's center and appeared in a band of thunderstorms on the storm's southwestern quadrant. Infrared imagery from NASA's ...

ISS 'space truck' launch postponed: Arianespace

5 hours ago

The July 24 launch of a robot ship to deliver provisions to the International Space Station has been postponed "for a few days", space transport firm Arianespace said Friday.

Recommended for you

A new approach to creating organic zeolites

22 hours ago

Yushan Yan, Distinguished Professor of Engineering at the University of Delaware, is known worldwide for using nanomaterials to solve problems in energy engineering, environmental sustainability and electronics.

A tree may have the answers to renewable energy

Jul 23, 2014

Through an energy conversion process that mimics that of a tree, a University of Wisconsin-Madison materials scientist is making strides in renewable energy technologies for producing hydrogen.

User comments : 0