The effect of the entrance of an alkyl into the molecule of a substance is not constant; sometimes the action of the poison is weakened, sometimes strengthened. Thus, according to Stolnikow, dimethyl resorcin, C6H4(OCH3)2, is more poisonous than resorcin C6H4(OH)2. Anisol C6H5OCH3, according to Loew, is more poisonous to algæ, bacteria, and infusoria than phenol C6H5OH. On the other hand, the replacement by methyl of an atom of hydrogen in the aromatic oxyacids weakens their action; methyl salicylic acid
is weaker than salicylic acid
.
Arsen-methyl chloride, As(CH3)Cl2, is strongly poisonous, but the introduction of a second methyl As(CH3)2Cl makes a comparatively weak poison.
§ 25. In some cases the increase of CO groups weakens the action of a poison; thus, in allantoin there are three carbonyl (CO) groups; this substance does not produce excitation of the spinal cord, but it heightens muscular irritability and causes, like xanthin, muscular rigidity; alloxantin, with a similar structure but containing six carbonyl groups, does not possess this action.
Allantoin.