Comparative study of the strongest solid Lewis acids known: ACF andHS-AlF₃

Abstract

Aluminium chlorofluoride (ACF) and high-surface aluminium fluoride (HS-AlF3) can be considered as solid superacids based on several surface characterization techniques presented here.

A HF Loaded Lewis‐Acidic Aluminium Chlorofluoride for Hydrofluorination Reactions

“…This diminished surface area was as well observed in the case of HF‐loaded aluminium alkoxide fluoride, however, the sample was less affected, and a value of 100 m 2 g −1 was obtained . The re‐determined value for the pure ACF is in accordance with previous studies determined by the BET method (Table ) . These observations are confirmed by studies on the pore size distribution using non‐local density functional theory (NLDFT), where two distinct kinds of pores for ACF were identified (Figure ).…”

“…This large shift indicates that free Lewis acidic sites are still present on the HF‐loaded ACF, but in a very small amount. They are as strong as found for ACF since an absorption band with the same energy was found for the surface‐bound deuterated acetonitrile . However, the intensity of the bands is much lower for the HF‐loaded ACF sample than for ACF, which is in good agreement with the assumption that most of the sites are blocked by HF.…”

“…Among them, aluminium chlorofluoride (ACF, AlCl x F 3− x , x= 0.05–0.3, patented by Dupont) is of high interest, in part because of its large surface area and high Lewis acidity, which is comparable to the one of SbF 5 . Its properties and reactivity have been intensely investigated, showing that a variety of reactions can be mediated . For instance, H/D or Cl/F exchange reactions were reported at ACF .…”

The Acid Strength of the Lewis‐Brønsted Superacids – A QSPR Study

“…On the other hand, it seems obvious that the acid strength of Lewis-Brønsted systems depends on the acidity of the Lewis component. However, proper estimation of the Lewis acids' reactivity, their actual acid strength might require employing more advanced approaches, e. g., surface modelling including NH 3 -TPD (where TPD stands for temperature programmed desorption), DRIFTS measurements, FTIR-photoacoustic spectroscopy, as demonstrated by Calvo et al [24] Nevertheless, we believe that a simple computational technique of acid strength estimation regarding Lewis-Brønsted superacids studied in this work, based on evaluation of their Gibbs free deprotonation energy leads to reliable predictions that might be further used in QSPR modelling.…”

Facile Preparation of BaClxFy for the Catalytic Dehydrochlorination of 1-Chloro-1,1-Difluoroethane to Vinylidene Fluoride

“…Other metal fluorides, such as MgF 2 , AlF 3 and fluorinated Cr 2 O 3 were found to be catalysts for dehydrofluorination reactions [12][13][14]. Similar to the chlorination of AlF 3 to aluminum chlorofluoride (ACF), BaF 2 also tends to be chlorinated to BaClF by Cl species under reaction conditions [15]. Consequently, a rapid decrease in the conversion of HCFC-142b and selectivity to VDF was observed.…”