绿色化学-第四章.PPT

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1、Application of Designing Safer ChemicalsChapter 4第四章第四章 设计更加安全化学品的应用设计更加安全化学品的应用 4.1 Isosteric Replacement of Carbon with Silicon in the Design of Safer Chemicals 4.2 Designing Biodegradable Chemicals 4.3 Designing Aquatically Safer Chemicals4.1 Isosteric Replacement of Carbon with Silicon (用硅对碳进行等电

2、排置换用硅对碳进行等电排置换)in the Design of Safer ChemicalsSilicon is an Isostere of Carbon4.1.1 Silicon is an Isosteric atom of Carbon Common Features of Silicon and Carbongrouped in column 4A of the Periodic Tablehaving many chemical similarities ： tetravalent, tetrahedral, and form stable bonds with carbon.

3、金刚石金刚石碳化硅碳化硅Organic derivatives in which carbon is replaced by silicon generally have no intrinsic toxicity, in contrast with the other Group 4A elements germanium, tin, and lead. From a toxicity perspective, silicon is the only Group 4A element that is a suitable replacement for carbon. In addition

4、, silicon is an abundant, inexpensive element and one that is available in a variety of forms.organic silicon compounds is quite instable, for the Si-O is so strung that organic silicon compounds are easily oxidated after exposed in environment.Acetylcholine(乙酰胆碱乙酰胆碱)Urethane(尿烷尿烷)Muscarinic Antagon

5、istis（蝇覃碱拮抗剂）（蝇覃碱拮抗剂）Example 1ONH2NOCH3SiONH2OOOUrethanes are neutral analogs of the neuro-transmitter acetylcholine, and were found to be antagonists(拮抗药)of the latter.Interestingly, silane was much less toxic to mice than Urethane (carbon) with identical dose-response curves, and exhibited muscle

6、relaxant properties.CarbamateSilicon substituted Isostere of carbamate (Similar insecticidal effect, more degradable, less toxic to human and environment) Example 2 Carbamate insecticide and its silicon analog were found to have similar toxicity to the house fly. ONHCH3OONHCH3OSiONHCH3OONHCH3OSiDoub

7、le bonds to silicon, and three-membered rings containing silicon, are unstable to air and moisture Single bonds from silicon to heteroatoms such as nitrogen and oxygen are strong but can hydrolyze readily. The silicon-hydrogen bond is more polarized than the carbon-hydrogen bond. Polarization: SiH C

8、H In contrast to the carbon case, increasing the number of hydrogen on a silicon increases the ease of oxidation, and the parent silane (SiH4) is pyrophoric(发火的、生火的). Poly an analog of polyethylene that is rich in SiH2 groups has recently been reported to be air stableH2C=CH2 Ethylene: StableH2Si=CH

9、2 vinyl silane: unstableCH2 CH2 CH2 CH2 CH2CH2n Polyethylene: Stable For a subtle difference in atomic size exists for silicon and carbon , Important differences in chemical reactivity also exist. When silicon is proximal(最接近的) to unsaturation, as in a vinyl or allyl silane, the compounds are stable

10、, but unlike their carbon analogs they are subject to acid catalyzed silicon-carbon bond cleavage RSiH+SiRH2ORH+SiHOBreaking ofbond is easyHerein lies a potential avenue for the design of environmentally degradable products. 4.1.3 The degradation and oxidative metabolism of organic silicon compoundA

11、n important component of designing safer chemicals is predicting their environment fate, and both abiotic degradation（非生物降解） and biological oxidation can play a role. Isosteric substitution of carbon with silicon in many cases may enhance abiotic degradation and biological oxidation nCurrently the m

12、ajor environmental source of organosilane is silicone polymer （聚硅酮）(siloxanes), primarily polymers of 1,1-dimethyl silanediol. MO SiOH-nH2O+nH2OSiOnHODepolymerizes in the presence of water and soil to silicates finallyAbiotic Degradationn Furthermore labeling studies have shown that the methyl group

13、s can be photo-chemically cleaved from the silicon, with the final product being the naturally occurring silicates. Biological OxidationnEarly studies of microbial growth in the presence of permethyl siloxanes（硅氧烷）（硅氧烷） suggested that biological cleavage of silicon-carbon bonds could occur nMore rec

14、ent work has shown that microorganisms can utilize dimethy siloxanes as a source of carbon, and soil incubation of 14C labeled siloxanes has been found to release 14CO2 nPioneering work by Fessenden on the metabolism of organosilanes by mammals found that phenyl and alkyl silanes were oxidized very

15、much like their carbon analogs. nA notable difference, however, was found for dimethyl phenylsilane in which the silicon-hydrogen bond was rapidly oxidized in vivo Example 1： Silane Analogs of DDTExample 2：Organosilane Fungicides 4.1.4 Examples for the Design of Safer Chemicals Using Silicon Substit

16、ution for CarbonSilane Analogs of DDT nDespite the relative safety of DDT to mammals, its toxicity to other species and environmental persistence led to the ban(被禁止) of this important pesticide. nIn an early effort to design a more benign version of DDT, a number of silane analogs such as the DDD an

17、alog were prepared with the anticipation that these would be less environmentally persistent. Silane Analogs of DDTnThe presence of the readily oxidized silicon-hydrogen bond would have been one source of instability, both environmentally and in vivo.ClCHClClClClClSiHClClClClDDTDDD Organosilane Fung

18、icides nAs a novel entry into the class of triazole（三唑） fungicides（防真菌剂防真菌剂）nMeberg and coworkers prepared a series of silane analogs. One of these, flusilazole（氟氟苯代硅三唑苯代硅三唑） proved to be a highly effective crop fungicide（谷类防真菌） and is now a major commercial product. nCompound flusilazole is an inhi

19、bitor of sterol（甾醇） biosynthesis, similar to other triazole fungicides. nThe properties of this compound responsible for its field performance, including volatility, solubility, and movement within plants, have been described. Organosilane FungicidesnThe primary metabolite of flusilazole is the sila

20、nol, resulting from cleavage of the triazole-substituted methyl group from silicon.n Presumably silanol has little or no biological activity, and the higher oxidation level silanol will enhance the rate of its further degradation (relative to flusilazole). Flusilazole is an excellent example of the

21、commercial potential for biologically active organosilanes. FlusilazoleFlusilazole （氟苯代硅三唑）（氟苯代硅三唑）MetabolismUsageUsage： crop fungicide 4.2 Designing Biodegradable ChemicalsExamples of Designing BiodegradableChemicalsThe Microbial Basis of Biodegradation Chemical Structure and Biodegradability Group

22、 Contribution Method for Predicting Biodegradability Chemicals: (resist biodegradation) exert possible toxic effect to biota，hardly to predict their potential toxic effect (at the time of release to the environment).Moreover, some bio-accumulative chemicals seemsafe according to toxicity criteria, b

23、ut have chronic(慢性的) or other unforeseen toxic effect Microbial degradation is the major loss mechanism for most organic chemicals in aquatic(水的) and terrestrial（陆地） environments, and is the cornerstone of the modern wastewater treatment plant.4.2.1 The microbial basis of biodegradation The key role

24、 in biodegradation: Microorganisms（primarily bacteria 细菌 and fungi真菌）are by far the most important agents of biodegradation in nature. An abundance of evidence exists to show that microorganisms are responsible for the degradation of many organic chemicals cannot be altered significantly by higher o

25、rganism.chemicals that they cannot metabolize;tend tochemicals into water insoluble; The eventual mineralization of organic compounds (their conversion to inorganic substances such as CO2 and water) can be attributed predominantly to microbial degradation. The process of biodegradation1.1.An organic

26、 compound must first enter the microbial cell through the cell membrane. (This may occur by passive diffusion or with the assistance of specific transport systems) Especially: for aquatic and terrestrial environments low levels of organic substrate and other nutrients.For large polymeric substrates:

27、 proteins, polysaccharides(多糖多糖), biodegradated by extracellular(细胞外酶细胞外酶)enzymes, 2.2.Once inside the cell, the reactions that a compound may undergo are determined by its molecular structure, hundreds of transformations have been described in the literature, but almost all can be classified broadl

28、y as： oxidative; reductive; hydrolytic; conjugative reactions In additionThe catabolic pathways employed by microbial populations are also diverse and vary with theenvironmental conditionsmicrobial degradation strategy is stepwise degradation to yield one or more intermediate products capable of ent

29、ering the central pathways of metabolism. The overall objective is always to produce carbon and energy for growth.The strategy of microbial degradation Naturally occurring organic compounds are degradable via pathways that represent evolutionary adaptations to prevailing conditions.Daley has said：“i

30、t is reasonable to believe that every biochemically synthesized organic compound is biodegradable.”4.2.2 Relationship between chemical structure and bio-degradabilityThe following molecular features generally increase resistance to aerobic biodegradation 1.Halides(卤代物）; especially chlorine and fluor

31、ine;2.Chain branching（支链物质）, especially quaternary carbon（季碳）and tertiary nitrogen, or extremely branching such as in surfactants derived from tri-or tetra propylene;3. Nitro, nitroso（亚硝基）, azo （偶氮基）, arylamino （芳氨基）;4. Polycyclic residues（多环残基）(such as in polycyclic aromatic hydrocarbons（多环芳香烃）or P

32、AHS（稠环芳烃）), especially with more than three fused rings;5. Heterocyclic residues（杂环残基）; e.g., pyridine rings（吡啶环）; 6. Aliphatic ether (C-O-C) bonds（脂肪族醚键）;7. High-substituted compound is more difficult to degrade than low-substituted one. For the most part, the features listed above affect the abili

33、ty of the compound to serve as an inducer or substrate, or both, of degradative enzymes and cellular transport systems. The chemical structures which favor biodegradability1.by the presence of potential sites of enzymatic hydrolysis (e.g., esters酯, amines胺); 2.by the introduction of oxygen in the fo

34、rm of hydroxyl(羟基), aldehydic (醛基) or carboxylic(羧基) acid groups; 3.by the presence of un-substituted linear alkyl chains (especially 4 carbons) and phenyl rings, which represent possible sites for attack by oxygenases.4.Lower-substituted compoundsThe first step of biodegradation is some kind of oxi

35、dation reaction. The second factor is particularly important because the first step in the biodegradation of many compounds (e.g., hydrocarbons) is the enzymatic insertion of oxygen into the structure, And this step is almost always rate limiting. The importance of inserting oxygen in the moleculeMo

36、re generally, if the first biodegradative step is some form of oxidation, it seems logical to expect that biodegrability will be enhanced if the synthetic chemist has already carried it (oxygen inserted) out during molecular design. .The solubility and bio-degradabilityThe number of substituted grou

37、ps attached to the main structure of the molecule and the aqueous solubility of the molecules alter significantly the biodegradability. The possible effects of solubility on biodegradability are as the following：1: Microbial bioavailability (微生物生物利用度微生物生物利用度) Insoluble chemicals tend to partition to

38、 the adsorbed state in activated sludge, sediments and soil. Most studies have shown that this tends to reduce the rate of biodegradation2： Rate of solubilization (溶解速度溶解速度)pMost studies have shown that for solid with very low solubility, only the dissolved or dispersed phase is available to microor

39、ganisms. pTherefore, the rate of dissolution of a solid in water may control the rate of biodegradation. pMany microorganisms excrete biosurfactants (e.g., rhamnolipids,鼠李糖脂鼠李糖脂) that enhance the rate of solubilizition. 3：Low aqueous concentration Some studies have shown that for chemicals soluble t

40、o the extent of only a few micrograms per liter or less, this concentration may be too low for optimal function (无法发挥其最佳功能无法发挥其最佳功能) of cellular enzymes(细胞酶细胞酶)or transport systems(传输系统传输系统). Thus the biodegradability is limited.4.2.3 Examples of designing biologically safer chemicalsExample 1Linear

41、 alkyl benzene sulfonate（直链烷基苯磺酸（直链烷基苯磺酸, LAS）What will happen with highly branched hydrocarbons ?Environmental problem TPBS were found to be incompletely biodegraded in municipal sewage treatment systems(城市污水处理系统）.TPBS was degraded by only about 50 % in sewage treatment units and as a result excess

42、ive foaming occurred in activated sludge aeration (通风) tanks, as well as in receiving rivers. LASLASCH3SO3HCH3 ( CH2)n ,n=7-11Eventually methods were developed that permitted the economical manufacture of a more environmentally acceptable product LAS, LAS surfactants could be completely degraded in

43、more than 50 years ago, Domagk found that the toxicity of simple quaternary ammonium compounds (QACS) were greatly enhanced by the presence of a long alkyl group (长链烷长链烷基）基）.Example 2 DialkylQuaternaries（二烷基季铵盐）（二烷基季铵盐）Dialkyl QuaternariesAccording to Cross, 66 % of the market for QACs is dominated

44、by three classes, all of which are dialkyl quaternaries, meaning that hydrophobicity (疏水性) is imparted to the molecule by two linear alkyl chains in the C9 to C17 range. 1）di-alkyl dimethyl ammonium salts（二烷基二甲铵盐）（二烷基二甲铵盐）2) imidazolium quaternary ammonium salts（咪唑季铵盐）（咪唑季铵盐） NNCH3(CH2)nCH3n=14-16H+

45、N(CH2)nCH3O3) ethoxylated ethan aminium quaternary unmonium salts（羟乙基乙铵鎓季铵盐）（羟乙基乙铵鎓季铵盐）CH3(CH2)nNNCH3H ON(CH2)nCH3OOn=14-16HH+nUntil recently the fabric softener market was dominated by a QAC of the first type, dihydrogenated tallow(动物脂) dimethyl ammonium chloride (DHTDMAC二氢化动物脂二甲基氯化铵) The long alky

46、l groups in DHTDMAC are derived from purified animal fat (tallow), and consist of a mixture chiefly in the C16-C18 (tallow fatty acids) range. nThe true aqueous solubility of DHTDMAC is exceedingly low, and the chemical sorbs strongly to solids in wastewater treatment and the environment. Removal in

47、 treatment is therefore high ( 95 %), unlike TPBS, but does not necessarily conespond to ultimate biodegradation. Example 3 Alkylphenol Ethoxylates（烷基酚乙氧基化物）（烷基酚乙氧基化物） (OCH2CH2)CH3CH3CH3CH3OHnn=12-14 The environmental risks associated with APEs and especially NPE are a complex and contentious issue.

48、Debate Most attention has focused on the mono- and diethoxylated nonylphenol adducts NP1EO (n = 1) and NP2EO (n = 2), which have been reported to be relatively stable intermediates in NPE biodegradation.CH3OCH2CH2OHCH3CH3CH3NP1EONP2EOCH3OCH2CH2OCH2CH2OHCH3CH3CH3nNP1E0, NP2E0 and nonylphenol（壬基酚） its

49、elf are highly toxic to aquatic organisms, whereas the parent NPEs (the number of ethoxylate groups may be as high as 30-50, but 12-14 is more typical) are much less toxic. nRecently added to this is a new controversy, as nonylphenol, NP2EO and related compounds have been reported to be estrogenic(雌

50、性激素的) in fish. APE% Biodegradation LinearBranchedC8AEE97146C8A P E9：containing 9 o x y - e t h y l group5149C9APE96525C9APE9：containing 9 oxy-ethyl group65308855573366327506210601805008975Table 4-1 Degradation of APETable 4-1 Degradation of APE4.3 Designing aquatically safe chemicals氧气、碳氢化合物光合作用哺乳动物