Flavouring agent Being an analog of pyridine, isoquinoline is a weak base, with a pKb of 8.6. It protonates to form salts upon treatment with strong acids, such as HCl. It forms adducts with Lewis acids, such as BF3.; Isoquinoline is a colorless hygroscopic liquid at room temperature with a penetrating, unpleasant odor. Impure samples can appear brownish, as is typical for nitrogen heterocycles. It crystallizes platelets that have a low solubility in water but dissolve well in ethanol, acetone, diethyl ether, carbon disulfide, and other common organic solvents. It is also soluble in dilute acids as the protonated derivative.; Isoquinoline is a heterocyclic aromatic organic compound. It is a structural isomer of quinoline. Isoquinoline and quinoline are benzopyridines, which are composed of a benzene ring fused to a pyridine ring. In a broader sense, the term isoquinoline is used to make reference to isoquinoline derivatives. 1-Benzylisoquinoline is the structural backbone in naturally occurring alkaloids including papaverine and morphine. The isoquinoline ring in these natural compound derives from the aromatic amino acid tyrosine.