What is the difference and connection between salicylic acid and aspirin

The chemical name of salicylic acid is o-hydroxybenzoic acid, with the molecular formula C7H6O3 and a relative molecular mass of about 138. It is a colorless needle-like crystal that readily sublimes and can volatilize with water vapor. It has the chemical properties of both phenols and carboxylic acids, gives a purple color in reaction with ferric chloride, and because of the influence of the phenolic hydroxyl group, its acidity is stronger than that of benzoic acid. Salicylic acid was originally used in dermatology and was first extracted from willow trees. It has a history of nearly a hundred years since its introduction. Clinically, salicylic acid at various concentrations has been widely and safely used, and is even called a sharp tool in dermatology. Salicylic acid can promote keratin metabolism, continuously and gently loosen dull, withered cells on the skin surface, has the best effect on clearing the skin layer, can normalize the process of skin metabolism, help revitalize cell regeneration, and accelerate the renewal of skin cells. In addition, salicylic acid itself has bactericidal ability, and its sodium salt can be used as a preservative for foods and the like. Salicylic acid is also a raw material for preparing drugs. For example, salicylic acid reacts with acetic anhydride to give acetylsalicylic acid, commonly known as "aspirin," which is a commonly used pain-relieving and fever-reducing drug. Aspirin (acetylsalicylic acid) can treat colds, relieve pain and reduce fever, and also has a good effect on preventing blood clots. The effective pharmacological component of aspirin is acetylsalicylic acid, and its molecular formula is C9H8O4. When aspirin is grafted with polymethacrylic acid via a diol, the following relationship exists between its performance and molecular structure: at this time, the hydrolytic performance of the entire graft (that is, the performance of undergoing hydrolysis to release the pharmacologically effective acetylsalicylic acid) is related to m in O(CH2)mO in the graft. When m increases from m=2 to m=7, the hydrolytic performance of the graft increases sharply, that is, the speed at which it releases acetylsalicylic acid accelerates. If the value of m can be controlled, then the release rate of acetylsalicylic acid is also controlled. For treating disease, one always hopes that this drug will become a long-acting drug, that is, that it can continuously and slowly release acetylsalicylic acid, so that acetylsalicylic acid can exist in the human body for a longer time for antithrombotic treatment. This is the origin of taking one dose to last many days. From the grafting of aspirin to turning it into a long-acting drug, one cannot help but greatly admire the intelligence and talent of chemists. (Author: Chen Gang)