In the process of metamorphic reaction, it only causes the exchange of atoms between coexisting minerals, without changing the atomic number of related minerals
Exchange reaction is the process of metamorphic reaction, which only causes coexistencemineralThe exchange of atoms (mainly Mg and Fe) between minerals without changing related mineralsAtomic numberA metamorphic reaction of.Because the exchange reaction does not change the atomic number of the mineral concerned, it only causessystemThe volume change is very small, and the pressure has little effect on the equilibrium. The distribution coefficient of Fe and Mg between coexisting minerals is a linear function of temperature, so the exchange reaction is goodGeothermometer。
1. Chemical reaction of one simple substance with one compound to form another simple substance and another compound, such as exchange reaction between active metal and acid or salt:
2. One of the basic types of inorganic chemical reaction, which refers to the reaction between one single substance and one compound to form another single substance and another compound, and can be expressed as: A+BC → B+AC
Exchange relation refers to the substitution of some element of a compound by the element of a simple substance.
classification
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According to the types of reactants and simple substances in products, exchange reactions can be divided into the following four situations:
1. The more active metal exchanges out the less active metal or hydrogen, such as:
Fe+CuSOfour=Cu+FeSOfour
Zn+2HCl=Htwo↑+ZnCltwo
2. The more active nonmetals are exchanged for the less active ones, such as:
Cltwo+2NaBr=Brtwo+2NaCl
Otwo+2HtwoS=2S↓+2HtwoO
3. Exchange of nonmetal to metal;
4. Metal exchange out of nonmetal:
The exchange reaction in solution or between gases is carried out at room temperature, and the exchange reaction between gas and solid or between two solids is generally carried out at high temperature.Electron transfer occurs in exchange reaction, both belong toRedox reaction。
Transesterification reaction with different catalysts
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SelectionStannous octanoate[Sn(Oct)two]AndTetrabutyl titanate(TBT) as polylactic acid (PLA)/Polypropylene carbonate(PPC)Composite catalystCatalysis of PLA/PPC transesterification.Through the analysis of the molecular structure, thermodynamics and rheological behavior of the reaction products, it was found that the transesterification reaction occurred between PLA and PPC molecules, accompanied by chain breaking reaction, whether under the action of a single catalyst or a composite catalyst.Where, when Sn (Oct)twoAs a single catalyst or Sn (Oct)two/When TBT is used as a composite catalyst, the sample is more prone to chain breaking reaction than significantTransesterification。Further analysis of pure sample in catalyst Sn (Oct)twoOr TBT. It is found that PPC mainly breaks the high molecular chain at the initial stage of the reaction, and will undergo obvious unzipping degradation, resulting in the low degree of ester exchange reaction of PLA/PPC at the same mass ratio, which provides a way to better study the ester exchange reaction of PLA/PPC.[1]
Catalytic effects of different catalysts on intermolecular transesterification
Whether only Sn (Oct)twoOr single catalytic system of TBT catalyst or Sn (Oct)two/In the TBT composite catalytic system, the solid residue does not show the proton peak of methylene (δ 5.00) and the proton peak of methylene (δ 4.18) in the PPC repeating unit, that is, there is no PPC chain segment in the solid residue. The reason for this result may be that the PLA/PPC does not undergo intermolecular ester exchange reaction, or the PLA used in the experiment is still soluble in acetone due to its low optical rotation,As a result, the product PLA-b-PPC generated by the reaction can be soluble in acetone and not exist in the solid residue.Therefore, NMR analysis of the solid residues and soluble substances extracted from the AC-0.5ST sample shows that there is only PLA in the solid residues, while there is a certain amount of PLA in the soluble substances, in addition to the PPCs that are easily soluble in acetone, which indicates that the PLA used in the experiment can be partially dissolved in acetone,As a result, the product PLA-b-PPC generated by transesterification reaction can also be dissolved in acetone but not in the solid residue, so there is no chemical shift of hydrogen in the PPC repeating unit in the nuclear magnetic spectrum of the solid residue.[1]
The number average molecular weight, weight average molecular weight, molecular weight distribution index and high molecular weight (>60.0 × 10) in the molecular weight distribution curve of PLA/PPC reaction system catalyzed by different catalystsfour）And low molecular weight (<2.0 × 10four）It can be found from the distribution percentage statistics that, compared with AC-0, the content of AC-0.5S and AC-0.5T in the high molecular weight part of samples increased by 3%, compared with that reported by Behravesh et alTransesterificationThe research results of producing higher molecular weight copolymers are consistent, which indicates that the single catalyst Sn (Oct)twoOr TBT catalysis, the transesterification reaction did occur between PLA and PPC.Among them, the molecular weight of sample AC-0.5T increased significantly, indicating that the PLA/PPC transesterification reaction degree was higher under the action of TBT.[1]
Analysis of transesterification reaction mechanism
Under the reaction condition of PLA/PPC mass ratio of 1:1, whether Sn (Oct)twoBoth the single catalytic system and the composite catalytic system of TBT and TBT can catalyze the transesterification of PLA/PPC to a certain extent, but at the same time, it will be accompanied by the chain breaking reaction of PLA or PPC molecular chain. Among them, the chain breaking reaction of the composite catalytic sample is more significant.But Sn (Oct)twoTBT and TBT have different catalytic effects on PLA or PPC. Among them, PLA has different catalytic effects on Sn (Oct)twoUnder the catalysis of TBT, a significant chain breaking reaction can take place, while under the catalysis of TBT, the main reaction is molecular lactone exchange;Sn(Oct)twoOnly a small number of high molecular weight chains of PPC have catalytic chain breaking effect, but TBT can catalyze significant chain breaking reaction of PPC molecular chain, indicating that chain breaking reaction of PPC mainly starts from high molecular weight chains.In the reaction process of equal mass ratio of PLA/PPC, if the catalytic effect of catalyst on PPC is not significant,Only a small amount of high molecular weight molecular chains of PPC participate in the reaction, so there are fewer active points for the transesterification reaction between PPC and PLA, and PPC will undergo unzipping degradation. Therefore, when the PLA/PPC mass ratio reaction is equal, the chain breaking reaction is generally better than the transesterification reaction. Only under the strong catalytic effect of TBT,With the increase of reactive sites of PPC, the reaction probability between PPC and PLA increases, and the degree of transesterification reaction increases.[1]
Effect of sodium ion substitution on hydrogen deuterium exchange reaction in gas phase
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Using linear ion trap-Time of Flight Mass SpectrometryPentaalanine (5Ala – nH+nNa) H, a simple polypeptide molecule substituted by different number of sodium ions, was determined in the gas phase+，n=The hydrogen deuterium exchange reaction of 2, 3, 4, 5, the rate of hydrogen deuterium exchange reaction of molecular ions replaced by different number of sodium ions and the amount of hydrogen deuterium exchanged were obtained, and the influence of the number of sodium ions on the molecular hydrogen deuterium exchange reaction was studied.[2]
Na Number in Molecules and HD Exchange Reaction
The H on the – NH group of 5Ala molecule will probably be replaced by Na at a ratio of 1:1 to generate Na generation polypeptide molecular ions.The Ala-Ala-Ala-Ala-Ala-Ala molecule contains five N atoms connected with six H atoms that can be replaced by Na.In addition, the H on the – COOH group at the end of the molecule may also be replaced by Na.That is, there are 7 H that can be replaced by Na, so ion products containing 2-5 Na atoms were observed in the experiment.
For 5Ala ions with different number of Na, the speed of H/D exchange reaction is obviously different. For example, after 200ms of H/D exchange process, (5Ala-2H+2Na) H+Basically no H/D exchange occurs, or only one H at most occurs partial exchange reaction, although (5Ala-2H+2Na) H+The ion contains up to 5 exchangeable H under experimental conditions;(5Ala-3H+3Na) H with 4 exchangeable H+1~4 H ions were exchanged;(5Ala-4H+4Na) H with 3 exchangeable H+2~3 H ions were exchanged;(5Ala-5H+5Na) H containing 2 exchangeable H+The ion exchanged 1~2 H.Under the same reaction conditions, different ions have significantly different H/D exchange reaction speed and exchange degree.It can be seen that the substitution of Na changes the H/D exchange properties of ions.[2]
-1H means (5Ala nH+nNa) H+The change of ion with exchange time after losing one H,nH indicates the number of exchanged H.For example, - 1H represents (5Ala nH+nNa) H+The ion loses an H with the change of exchange time, which decreases the fastest, indicating that an H in the ion is exchanged soon.1H first increased rapidly and then decreased gradually, indicating that the ion exchanged one H quickly at first, but then exchanged two H, so 2H will rise with the decrease of 1H.Due to the further exchange, 1H and 2H will decrease, and 3H will increase until more and more H are exchanged.
The speed and extent of the H/D exchange reaction of molecules are directly related to the molecular conformation and proton affinity potential. The change of these two molecular properties will lead to the change of the H/D exchange reaction properties.[2]
Influence of q value of linear quadrupole field on molecular HD exchange reaction
Linear quadrupoleqThere are two possible ways to influence the ion hydrogen deuterium exchange reaction, one is due to the differentqThe temperature is different, so it will have a molecular configuration corresponding to a certain temperature.Generally speaking, at higher temperatures, the molecular structure will be relatively "loose", which is more conducive to the occurrence of H/D exchange reaction.in other words,qValue affects H/D exchange by affecting molecular configuration;The second is that the temperature of ions will change withqFor some H/D exchange reactions with certain activation energy, the increase of temperature is obviously conducive to the occurrence of the reaction and the increase of the reaction speed.I.eqThe H/D exchange reaction rate can also be affected by the temperature of the reaction molecules.[2]
(5Ala-3H+3Na) H+H/D exchange reaction of ions andqThe change relationship of the value has similar results for the influence of other ions.To illustrate the problem, only the experimental results of one ion are given here.
WhenqWhen<0.8, it has little effect on the H/D exchange reaction of ions, but whenq>At 0.8, it has a significant impact on the H/D exchange reaction of ions, which significantly accelerates the reaction rate and the amount of exchange.5Ala molecule belongs to a relatively small system. Although the configuration of its molecule under different conditions will be different, it will not change much. In other words, it can be considered that the influence of the change of ion configuration on the ion H/D exchange reaction is not decisive here, so the obvious change of H/D exchange reaction is more due toqThe increase of the value changes the temperature of the ions.It should be noted here that,qIncreasing the value does not change DtwoTemperature of O molecule, because DtwoO is not charged, so its motion state is not affected byqThe effect of value changes.In conclusion, it is believed thatIon exchange reactionSpeed is affected byqThe main reason for the influence of pH value is the increase of ion temperature, not the change of ion configuration.[2]
