Off a Dekang RY4 bottle, carrying the warning "Very toxic by inhalation, in contact with the skin and if swallowed" and bearing a skull and crossbones symbol, the ingredients are:
Propylene glycol (75%) 3-methylcyclopentane-1.2-dione (2.5%) 1-malic acid (3%) 2.3.5.6 tetramethylpyrazine (1.5%) 2.3.5-trimethylpyrazine (0.3%) beta-dainescenaone (?) (0.2%) acetylpyrazine (0.2%) 2-acetylpyradine,ethanol (10%) rhodium (0.3%) vanillin (2.5%) ethyl acetate (0.5%) ethyl maltol (1.0%) 2-methyl-butyric acid (0.5%)
Googling the components I find:
Propylene glycol: Obvious.
3-methylcyclopentane-1.2-dione (aka Cyclotene): Flavour: caramel; maple; smoky; coffee; nutty; bready; liquorice. Safe.
Malic acid: Found in all fruits. Taste: mellow, smooth, persistent sourness. Universal flavour enhancer. Healthy.
2.3.5.6 tetramethylpyrazine: Used in flavour concentrates. Dependant on manufacturer, tastes like: Cocoa, roasted peanuts, Coffee, fermented soybean and/or chocolate and is used to flavour these products. Safety rating: Harmful if swallowed.
2.3.5-trimethylpyrazine: Same as above plus flavour: Caramel, Baked potato and peanut butter. Safety rating: Toxic if swallowed, irritating to respiratory system, eyes, skin. Flammable.
Beta-dainescenaone: Thats what it looked like after I messed juice on the label, but probably beta-damascenone. Flavour: Intensely fruity odour with plum, berry, sugary and rose nuances. Also: woody, floral, herbal, green and fruity, spicy tobacco, apple; herbaceous; nutty; citrus; smoky; wine-like. Safety rating: Irritant. Irritating to respiratory system, eyes, skin.
2-acetylpyradine ethanol: Flavour: Sweet, nutty, tobacco, popcorn. Safety rating: Toxic if swallowed, irritating to respiratory system, eyes, skin.
Rhodium: Flavour: Sweet floral woody. Safety rating: Irritant. Irritating to respiratory system, eyes, skin.
Vanillin: Synthetic vanilla.
Ethyl acetate: Used in flavour concentrates and perfumes. Sweet, fruity, vinegary smell. Found in wines. Also a flammable solvent. Low toxicity.
(This is a solvent!!)
Ethyl maltol: Flavor enhancer used in wine, chocolate, vanilla, fruit flavoured drinks, pastries, candy, tobacco, cosmetics, and medicines. Used because it tends to mask bad tasting chemicals, and heightens richness and creaminess. Safe.
2-methyl-butyric acid: Flavour: apple; apricot; cheese; chocolate; grape; fruity; pineapple; sour; strawberry; woody; wine-like. Safety rating: Corrosive: Harmful to skin and if swallowed.