REAGENTS
ATMOSPHERIC CHEMISTRY
▸ Quick and easy acyl fluorides Tetramethylammonium trifluoromethylthiolate, [N(CH3)4]SCF3, is a mouthful to say, but the inexpensive, bench-stable, and easy-to-use salt has been impressing chemists over the past few years for its versatility in adding SCF3 groups to molecules and as a fluorinating reagent. For example, Franziska Schoenebeck and her group at RWTH Aachen University have shown that [N(CH3)4]SCF3 has untapped potential as a fluorinated surrogate of thiophosgene (SCCl2), using it to functionalize alcohols and amines. Going further, Schoenebeck’s group has now used the trifluoromethylthiolate salt to convert aromatic and aliphatic carboxylic acids to acyl fluorides, which themselves are useful reagents (Org. Lett. H3C
O
F3C S–
H3C
R
+
N
CH3 CH3
O R
OH
F
Tetramethylammonium trifluoromethylthiolate, [N(CH3)4]SCF3, is proving to be a versatile SCF3 transfer reagent and fluorinating reagent, as shown in this new reaction with carboxylic acids.
C R E D I T: N ASA ( OZO N E ) ; ACS NA NO ( Mn PS 3 )
2017, DOI: 10.1021/acs.orglett.7b02516). The appeal of using [N(CH3)4]SCF3 to fluorinate carboxylic acids is its ability to replace specialized reagents derived from SF4. Those reagents often are toxic and corrosive, require additives, and tend to have poor functional-group tolerance and selectivity leading to undesired by-products. The trifluoromethylthiolate salt, first reported years ago but little used until recently, does away with those problems. Schoenebeck says her team has had “quite a lot of interest” from industry and other academic groups about using [N(CH3)4]SCF3, which could lead to efforts by her group to commercialize it.—STEVE RITTER
2-D MATERIALS
▸ Manganese thiophosphite joins 2-D materials club Examples of materials measuring just a few atoms thick have been popping
Chlorocarbons remain a threat to Earth’s ozone layer The Montreal Protocol, which went into effect in 1989, led to the phaseout of a suite of chlorofluorocarbons and related halocarbons. Although useful as refrigerants, propellants, and fire-extinguishing agents, these chemicals were found to be destroying Earth’s atmospheric Images of Earth’s ozone ozone layer, which helps protect the planet hole show how it grew from from harmful solar UV radiation. The treaty being modest in 1979 (left), and its revisions have reduced atmospheric significant in 1999 (center), concentrations of the problematic chemicals and is recovering in 2017 (right); purple and blue so that the ozone layer, which reached a low indicate the least ozone, and point in thickness in the 1990s, has begun to yellow and red the most ozone. heal—ozone depletion is starting to look like a problem solved. But new measurements from Southeast Asia reported by an international team led by David E. Oram of the University of East Anglia have revealed that increasing emissions of some halocarbons not regulated by the Montreal Protocol are threatening to slow or possibly reverse the recovery (Atmos. Chem. Phys. 2017, DOI: 10.5194/ acp-17-11929-2017). In particular, concentrations of 1,2-dichloroethane, used to make poly(vinyl chloride), and dichloromethane, used as a paint stripper and process chemistry solvent, have been rising over the past decade because of growing industrial activity in China and other countries in the region. These chemicals were thought to be too short-lived to reach the stratosphere in significant amounts, so they were not included in the treaty. The rising emissions in Southeast Asia are concerning, Oram explains, because prevailing winds carry the compounds to the tropics, where they more easily rise into the atmosphere and can do damage. “We are highlighting a gap in the Montreal Protocol that may need to be addressed in the future, particularly if atmospheric concentrations continue to rise,” Oram says.—STEVE RITTER
up so quickly in recent years that many categories of materials now have several members in the two-dimensional materials club. The list includes organics, inorganics, and single-element varieties representing a large group of electrical conductors, insulators, and semiconductors with impressive mechanical, thermal, and optical properties. Magnetic members were noticeably absent until just a few months ago, when two chromium compounds joined. The two lone mag-
MnPS3, an antiferromagnetic material, has been prepared as atomically thin flakes. Mn is pink; S is yellow; P is gray.
netic members have now been joined by a third one—manganese thiophosphite, MnPS3 (ACS Nano 2017, DOI: 10.1021/ acsnano.7b05856). Similar to refrigerator magnets, the chromium compounds are ferromagnetic, meaning their magnetic moments, or spins, point in the same direction. MnPS3 is a 2-D antiferromagnetic material: The up and down orientations of its spins alternate from one atomic site to the next. Gen Long and Ning Wang of Hong Kong University of Science & Technology and coworkers synthesized flakes of the compound as thin as two atomic layers from a mixture of the elemental powders via a high-temperature method. For now, the ultrathin material provides mainly a means to probe antiferromagnetism in 2-D. In the future, these kinds of materials may be used in cloaking applications that make magnetic data-storage devices and their data invisible.—MITCH JACOBY OCTOBER 30, 2017 | CEN.ACS.ORG | C&EN
7
