the disadvantage of grignard reagents is that they readily react with protic solvents (such as water), or with functional groups with acidic protons, such as alcohols and amines. atmospheric humidity can alter the yield of making a grignard reagent from magnesium turnings and an alkyl halide. one of many methods used to exclude water from the reaction atmosphere is to flame-dry the reaction vessel to evaporate all moisture, which is then sealed to prevent moisture from returning. chemists then use ultrasound to activate the surface of the magnesium so that it consumes any water present. this can allow grignard reagents to form with less sensitivity to water being present.