Cyclization means open chainorganic compoundThe process of transforming into organic compounds with closed loop structure.
Containing three or more double bondsPolyunsaturated fatty acidsIn heating, alkali isomerization, catalytic hydrogenation and other reactions, self cyclization will occur to generate cyclized fatty acids.If linolenic acid ester is heated to 225 ℃~295 ℃ in ethylene glycol solution orsodium hydroxide84kg/cm in aqueous solutiontwoAt 300 ℃, the product contains a certain amount of 1,2-disubstituted cyclohexadiene.
Tungic acid、linolenic acid, linoleic acid, etc., will be cyclized in heating, alkali isomerization, catalysis and other reactions.The cyclization of methyl tungate started at 180 ℃.After the linear chain compound is separated from urea, it is confirmed that the cyclized monomer is halogenated, the hydrogen halide is removed from the aromatization, and then oxidized to obtain phosphobenzoic acid.
Linolenate, linseed oil incarbon dioxideUnder protection, heat to 275 ℃ and keep for 12 hours to obtain monocyclic compound.The cyclite is toxic, so flaxseed oil heated to more than 220 ℃ is not suitable for eating. Usually, cooking temperature does not exceed this temperature.
Cyclic compounds are also found in alkali isomerized oil. For example, when flaxseed oil is heated to 295 ℃ by alkali isomerization, cyclized compounds can be obtained with a yield of 30-32%.If notglycolHowever, using water as solvent can also generate ring compounds, although the yield is less, the cost is low, and the cyclization catalysts include selenium and palladium.Nickel adsorbed on diatomite, plus 3% sulfur, can be used to prepare aromatic fatty acids with a yield of 7%.When hydrogenating animal and vegetable oils, if the amount of hydrogen is low, the temperature is high, and the degree of unsaturation of the oil is high, it is beneficial to generate rings.The cyclides in the hydrogenated oil do not contain double bonds.
Cyclic fatty acid containing double bond, used to make alkyd resin, superior to natural fatty acid, with shorter drying time, good hardness and resistance toChemical ReagentsStrong ability.Hydrogenated ringFatty acid esterIt is suitable for low temperature lubricant and oxidation resistance, as well as high-performance turbine and aircraft.Amides and amines made of cyclic saturated fatty acids have very low melting points. Some amides and nitriles can be used as plasticizers for ethylene plastics. Because they can form stable and transparent gels, cyclic alcohols can be used in cosmetics.[1]
Cyclization reaction
Announce
edit
stayOrganic compoundThe reaction of forming new carbon rings or heterocycles in molecules is called cyclization reaction, also called closed loop or cyclization condensation.When forming carbon ring, of course, cyclization reaction is completed by forming carbon carbon bond.When forming a ring structure containing heteroatoms, it can complete the cyclization reaction by forming a carbon carbon bond, or by forming a carbon heteroatom bond (C-N, C-O, C-S bond, etc.), or sometimes by bonding between two heteroatoms (N-N, N-S bond, etc.).For example:[2]
N-N bond cyclization reaction:
N-N bond cyclization reaction
C-C bond cyclization reaction:
C-C bond cyclization reaction
C-S bond cyclization reaction:
C-S bond cyclization reaction
There are many types of cyclization reactions, and many reagents are used, so there is no unified general reaction formula, nor can general reaction process and more systematic general laws be proposed.However, according to a large number of facts, we can conclude the following rules:
① Most cyclization reactions are formed by the reaction, bonding and connection between two molecules at the appropriate position, but no new ring structure has been formed.Then, a cyclization reaction takes place at an appropriate position inside the molecule to form a new ring structure.
② The aromatic six membered carbon ring and five membered and six membered heterocycles are relatively stable and easy to form.
③ Some cyclization reactions are reactions between two molecules at two appropriate positions at the same time, forming bonds to form a new ring structure. Such reactions are called synergistic reactions.Except for a few cyclization reactions that form a ring structure by double bond addition, most cyclization reactions always shed some simple small molecules when forming a ring structure.
④ To promote the aboveSmall moleculeIt is necessary to use condensation promoter for the shedding of.
⑤ To formHeterocycleOne of the starting reactants must contain heteroatoms.[2]
Cyclization replacement rearrangement
Announce
edit
Cyclization substitutionrearrangementIt is indicated by the symbol "rd" in the reaction formula. It is a cyclization reaction initiated by the position of free radicals. The original chemical bond breaks during the reaction（Free radicalIs replaced) and a new key is generated at the same time.Cyclic substitution rearrangement can be seen in long-chain alkyl compounds containing saturated heteroatoms.E.g. ω-ChlorododecaneChlorine in m/z 91 (100)Fragment ionAnd m/z 105 (25).
Although the ability of chlorine to give electrons is extremely weak in the reaction, the carbon chlorine bond generated can compensate for the energy required for the cleavage of the carbon carbon bond, which is beneficial to the reaction.
Brominated hydrocarbons with chain length greater than 6 carbon atoms can also lose R free radicals through cyclization replacement rearrangement, forming bromine containing five or six membered ring fragment ions, which are more stable.
Long chain alkyl halohydrocarbonmercaptan, thioethers and primary amine compounds also undergo cyclization substitution rearrangement, generating relatively stable cyclic fragment ions of sulfur and nitrogen.As shown in Figure 1:[3]
Fig. 1 Ring fragment ions
Cyclization polymerization
Announce
edit
The polymerization of unconjugated dienes to produce high cross-linked thermosetting products is an important process in industrial production, such as diallyl p-phthalate, bis (allyl carbonate)Diethylene glycolPolymerization of ester and diallyl maleate.However, the measured gel point of these systems is always higher than the theoretical prediction value, which is due to the intramolecular cyclization of diene monomer.That is, in the copolymerization reaction system, there is a competitive reaction of intermolecular crosslinking reaction (6.82) and intramolecular cyclization reaction (6.83).
Reaction (6.82) shows that monomer 6-4 polymerizes to form a linear polymer with double bonds as side groups, and the double bonds of side groups further react to formCross-linked polymer。At the same time, chain free radicals 6-5 will attack the side group double bonds in the molecule, forming ring chain free radicals 6-6 and 6-8 respectively, and further polymerizing to generate ring containing polymers 6-7 and 6-9.As the reaction (6.83) consumes the side group double bonds, the crosslinking degree of the polymer decreases.When copolymerized with monoene monomers, the copolymer structure is more complex.For example, intramolecular cyclization occurs before or after the second monomer is added to the diene unit at the end of the growth chain, and different ring structures will be formed.
Reaction diagram of cyclization polymerization
Not all diene monomers will undergo crosslinking reaction when they are polymerized.Some monomers, such as diallyl quaternary ammonium saltFree radical polymerizationA soluble non crosslinked product with almost no double bond was formed.This reaction is called intramolecular and intermolecular alternating polymerization, or cyclization polymerization, and the resulting polymer is a linear polymer with a ring structure in the main chain.[4]
The effect of cyclization on crosslinking depends on the size of the ring formed during polymerization.The degree of cyclization is in the following order with the size of the ring: five - and six membered rings>seven membered rings>larger rings.When five or six membered rings are formed, ring forming polymerization is the dominant reaction.For example, 1,6-dienes such as (methyl) acrylic anhydride, diallyl quaternary ammonium salt and allyl methacrylate (Z contains three ring forming atoms) can be cyclically polymerized to form a structural unit of five membered ring or six membered ring, or both.The formation of the five membered ring is controlled by the kinetic process, and the cyclization process is completed by secondary carbon free radicals;The process of forming a six membered ring via a relatively stable tertiary carbon radical belongs toThermodynamic controlProcess.Diallyl quaternary ammonium salt and divinyl acetal form five membered ring structure unit without exception;Acrylic anhydride forms five membered ring and six membered ring;Methacrylic anhydrideOnly a six element ring is formed as a structural unit.For the polymerization of acrylic anhydride, reducing the polymerization temperature and solvent polarity can greatly reduce the formation of five membered ring structural units;However, the cyclization polymerization of methacrylic anhydride is not affected by temperature and solvent polarity.
Intermolecular polymerization rate (Rp）Intramolecular cyclization rate (Rc）The relative size of is related to the monomer concentration, as shown in the following formula.
Rp/Rc=2kp[M·][M]/kc[M·] =2kp[M]/kc
Wherein, [M] is the concentration of diene monomer.It can be seen that increasing the monomer concentration is conducive to the chain growth reaction between molecules.Compared with intermolecular chain growth reaction, intramolecular cyclization reaction has higher activation energy and larger collision frequency factor. Increasing temperature and solvent polarity can improve the probability of cyclization polymerization.
Asymmetric dienes, such as allyl methacrylate, whose two double bonds have different activities, significantly reduce the possibility of cyclization.[4]
