How to pronounce“pentachloride”in English

and kicks a chloride ion off of phosphorous pentachloride.

This general definition doesn’t include compounds like phosphorous pentachloride that can be considered non-traditional Lewis acids, some of which we'll meet later in the series.

Then, we can react the carboxylic acid with phosphorus pentachloride or thionyl chloride to get an acid chloride – like we did in episode 30.

To solve this problem, we can convert the carboxylic acid to a more reactive functional group: an acid chloride, using either phosphorus pentachloride or thionyl chloride.