Through further research, the hydrolysis mechanism of NVP in the presence of acrylic acid or KSO was obtained.Vinyl charge imbalance in the NVP molecule, that is, the charge density on the two carbon atoms connected by double bonds is different.This charge imbalance provides the possibility for the hydrolysis of NVP, when there are acidic or alkali metal ions, the isomerization occurs in the NVP molecule, forming a series of transition states, and the lifelong generation of pyrrolidone and acetaldehyde, This is the first step of NVP hydrolysis, and the second step of NVP hydrolysis is the addition reaction of pyrrolidone generated in one step with NVP molecules, and then further decomposes into pyrrolidone and acetaldehyde with the participation of water. From the perspective of NVP hydrolysis mechanism, whether NVP can be hydrolyzed mainly depends on whether a series of transition states can be formed in one step, or whether the intramolecular isomerization reaction of NVP can occur is the key to NVP hydrolysis.
The presence of H* or alkali metal cation in solution enables the intramolecular isomerization of NVP, so the hydrolysis of NVP can be carried out. Obviously, pyrrolidone potassium salt is more likely to undergo addition reactions with NVP, resulting in a larger hydrolysis rate of NVP in the presence of K and SO.
Since NVP is easy to hydrolyze, two points should be paid attention to in the production and use of NVP: first, attention must be paid to removing water when synthesizing NVP to ensure that the product does not contain water; In the process of storage and transportation, to make the product neutral or weakly alkaline, so as to prevent hydrolysis and self-polymerization reaction, the usual method is to add 0.1% alkali such as sodium hydroxide, ammonia or low molecular weight amines.
The molecular weight of PVP is usually expressed by K value, according to the data provided by the German BASF company, when the K value is less than 30, its bulk density is 0.4~0.6g/ml, when the K value is 90, the PVP bulk density is 0.11~0.25g/ml. On the contrary, the smaller the molecular weight, the smaller the voids between PVP molecules when they are stacked together, and the atoms of different molecules can also fill the gaps between the atoms in the adjacent molecules, which leads to the increase of PVP density, that is, the bulk density increases when other conditions are the same. In addition, according to the information provided by ISP in the United States, the bulk density of PVP-K is about 0.3g/ml, which is quite different from the bulk density of similar products of BASF. In addition, different measurement methods will also lead to differences in PVP bulk density data. The bulk density of insoluble or cross-linked PVP is generally 0.28~0.38g/ml.
