MODEL RELEASED. Organic synthesis. Chemistry pupil heating a pear-shaped flask with a bunsen burner during the synthesis of bromobutane. This is a substitution reaction, where butanol is reacted with hydrogen bromide to form a halogenoalkane (1-bromobutane). The reaction is very volatile, so reflux techniques are utilized. A condensing tube (down left) that is cooled by cold flowing water (pipes, orange) returns evaporated reactants to the flask.