The Quantitative Determination of Hydroperoxides,Alcohols, and Ketones in Hydrocarbon Solvents

Abstract

Iodometric titration with the dead stop endpoint was used to determine the amount of alkylhydroperoxides in an oxidation reaction mixture composed of the hydrocarbon starting material, an alcohol, a ketone and an alkylhydroperoxide. Because alkylhydroperoxides decompose on glpc analysis, glpc could not be used for total analysis of the reaction mixture nor for the determination of the in situ alcohol content. However, the addition of triphenylphosphine to a separate portion of the sample quantitatively produced the corresponding alcohol from the hydroperoxide without interfering with the ketone concentration. The total alcohol content of this portion could then be determined by glpc, and the initial alcohol content found by subtracting the amount of hydroperoxide from the total alcohol.     

Study of the thermal oxidation of polyolefines—IX: Some differences in the oxidation of polyethylene and polypropylene

In the thermal oxidations of polyethylene (PE) and polypropylene (PP), both similarities and differences are found. In the initial stage, the ratio of the hydroperoxide formed and the amount of oxygen absorbed is independent of both the nature of the polymer and the actual reaction conditions. With increased conversion, however, this ratio decreases to a greater extent in the case of PE than for PP. Most of the carbonyl groups formed in the PE chain during oxidation are ketones and carboxyls, but in PP there are also carbonyls with different structure. The amount of carbonyl groups in PE is approximately 1.5 times that observed for PP. The number of scissions involving considerable molecular weight decrease is higher for PE than for PP: for identical conversions, the ratio of scissions is S_PE/S_PP ～ 6.     

Studies in reduction of molecular weight of polypropylene

Polypropylene (PP) is the most widely used polyolefin, due to its high mechanical strength and better processability in comparison to the others in its group. Conventional methods of polymerisation result in high molecular weights of PP. However, high molecular weights are not required for several applications. To overcome this problem controlled reduction in molecular weight of PP in presence of free radicals, in solution, is proposed. Four commonly available free radical generators viz: benzoyl peroxide (BPO), azo- iso-bis butyronitrile (AIBN), t-butyl hydroperoxide (TBHP) and dicumyl peroxide (DCP) were used to bring about reduction in molecular weight of PP. Effect of the free radical generator concentration, reaction time, reaction temperature and reaction medium (toluene, xylene and decalin) on the extent of molecular weight reduction was studied. The effect of this molecular weight reduction on mechanical, thermal, rheological and crystalline properties of the polymer was also studied. With proper selection of initiator and reaction conditions, it was possible to obtain low molecular weight branched PP with improved mechanical and thermal properties.     

非水滴定和傅立叶红外光谱在聚丙烯马来酸酐接枝物表征中的应用

采用非水滴定法中的无机碱直接滴定方法测定了马来酸酐在聚丙烯上的接枝率,并对该方法作了可行性验证,讨论了非水滴定中的两个难点：化学计量比的确定和滴定终点的判断。通过傅立叶红外光谱法(FTIR)对聚丙烯马来酸酐接枝物的纯化效果、自由基引发反应对非水滴定的影响及聚丙烯接枝马来酸酐的反应机理作了定性分析,并结合非水滴定的数据绘制了红外定量校准曲线。     

The analysis of combustion products : The effect of hydrogen peroxide on the reaction of potassium permanganate with organic peroxides in acid solution

Although methyl and ethyl hydroperoxides alone do not react with potassium permanganate in acid solution at room temperature, they can be oxidised by this reagent in the presence of hydrogen peroxide. The apparent equivalents (as compared with hydrogen peroxide) are much lower than usual but, in the presence of excess hydrogen peroxide, the titre due to the organic peroxide is proportional to its original concentration. This forms the basis of a simple titration method which, though empirical, is both rapid and accurate. Since t-butyl hydroperoxide does not react in this way, it may be possible to differentiate the higher peroxides from lower peroxides.     

THE FTIR STUDIES OF PHOTO-OXIDATIVE DEGRADATION OF POLYPROPYLENE

The photo-oxidative degradation process of polypropylene film containing iron ions was investigated via FTIR and absorbance substraction technique. It is shown that the iron ions play an important role in the decomposition of hydroperoxide and the increase of the degradation rate of polypropylene film. The amorphous region of PP film undergoes degradation prior to the crystalline one.     

Hydroperoxide build-up in the thermal oxidation of polypropylene - A kinetic study

The thermal oxidation of unstabilised polypropylene (PP) was studied at 80 °C under various oxygen pressures: 0.02, 0.5 and 5.0 MPa, and, under 5.0 MPa oxygen pressure at various temperatures: 60, 80, 100 and 120 °C. Hydroperoxides were titrated using a chemical titration method and modulated DSC (taking an enthalpy of −325 kJ mol⁻¹). Starting from a previous kinetic analysis of carbonyl growth in same exposure conditions, we have tried to simulate experimental results by a model based on the classical mechanistic scheme in which initiation results from POOH (mainly bimolecular) decomposition. The model, which takes into account substrate consumption and does not rely on usual simplifying assumptions (steady state for radicals, long kinetic chains, interrelations between termination rate constants), generates kinetic curves with the same shape as experimental ones and predicts well the effect of O₂ pressure and temperature on hydroperoxide and carbonyl concentrations.     

HIPS／PP熔融反应共混及其动态力学性质

研究了高抗冲聚苯乙烯（HIPS）／聚丙烯（PP）共混物在过氧化二异丙苯（DCP）存在下的熔融反应过程及其动态力学性质．HIPS在DCP存在下以聚苯乙烯（PS）的降解为主，伴随着聚丁二烯（PB）的交联和接枝，PP在DCP存在下以降解为主，HIPS／PP在DCP存在下以PP同HIPS的反应接枝为主，这种原位生成的增容剂显著地改善了HIPS／PP两组份间的相容性，其分子运动特征较前两者发生明显变化，PS的Tg下降，PB和PP的Tg升高．     

Degradability of linear polyolefins under natural weathering

High density polyethylene (HDPE), linear low density polyethylene (LLDPE), and isotactic polypropylene (PP) containing antioxidant additives at low or zero levels were extruded and blown moulded as films. An HDPE/LLDPE commercial blend containing a pro-oxidant additive (i.e., an oxo-biodegradable blend) was taken from the market as supermarket bag. These four polyolefin samples were exposed to natural weathering for one year during which their structure and thermal and mechanical properties were monitored. This study shows that the real durability of olefin polymers may be much shorter than centuries, as in less than one year the mechanical properties of all samples decreased virtually to zero, as a consequence of severe oxidative degradation, that resulted in substantial reduction in molar mass accompanied by a significant increase in content of carbonyl groups. PP and the oxo-bio HDPE/LLDPE blend degraded very rapidly, whereas HDPE and LLDPE degraded more slowly, but significantly in a few months. The main factors influencing the degradability were the frequency of tertiary carbon atoms in the chain and the presence of a pro-oxidant additive. The primary (sterically hindered phenol) and secondary (phosphite) antioxidant additives added to PP slowed but did not prevent rapid photo-oxidative degradation, and in HDPE and LLDPE the secondary antioxidant additive had little influence on the rate of abiotic degradation at the concentrations used here.     

三氯化铁对聚丙烯光氧化降解的作用

用红外及紫外光谱法研究了三氯化铁(FeCl₃)对聚丙烯(PP)光氧化降解的影响。实验结果表明,FeCl₃对聚丙烯光氧化有显著的促进作用,但促进作用与FcCl₃含量之间不成线性关系,存在一促进作用的极大值(在本实验条件下,FeCl₃含量为0.5%时,促进作用最大)。实验还表明,FeCl₃的作用可能包含了通过光解产生自由基引发PP光氧化反应、催化分解氢过氧化物以及光屏蔽等几种作用。根据FeCl₃的作用机理,解释了FeCl₃对PP光氧化降解的促进作用与其含量的依赖关系中存在的极位现象。     

Photostabilisation mechanisms in polymers: A review

Key degradative processes for various polymers are itemised, together with photostabilisation mechanisms which can minimise these processes. Polymers can be conveniently classified as inherent absorbers, which absorb large amounts of solar uv, and as ‘non-absorbers’, that is polymers transparent in the near uv. The former group which includes aramids, polycarbonates and polyesters is predominantly photodegraded by primary processes causing direct bond scission and stabilisation is best effected by the use of uv absorbing additives or opaque pigments. The ‘non-absorbers’ include polyolefins and poly(vinylchloride) which are degraded as the result of oxidative chain processes initiated by chromophoric impurities. For polypropylene the dominant photooxidation product is hydroperoxide which photocleaves to initiate further oxidation. Various uv. stabilisers for polyolefins appear to owe their effectiveness to their ability to decompose hydroperoxide groups and/or to their ability to scavenge free radical intermediates in the oxidative process.     

Photochemistry and Photobiology of Furocoumarin Hydroperoxides Derived from Imperatorin: Novel Intercalating Photo-Fenton Reagents for Oxidative DNA Modification by Hydroxyl Radicals*

Photochemical and photobiological properties of the im-peratorin-derived furocoumarin hydroperoxides la, la', 2a and 2a’have been investigated. Irradiation (350 nm) of the hydroperoxide 2a’afforded the alcohol 2b (2%), a diastereomeric mixture of the hydroxy epoxide 2c (40%; diastereomeric ratio = 80:20) and the epoxide 2d (8%). The formation of these products was rationalized in terms of homolysis of the hydroperoxide bond initiated by intramolecular energy transfer from the photoexcited furocoumarin chromophore. The quantum yields for the photolytic decomposition of hydroperoxides were estimated to be in the range of 0.03–0.85 and decreased in the order 2a ? 2a′? 1a′≥ 1a. The involvement of hydroxyl radicals in these reactions was established by trapping experiments with benzene and spectroscopic evidence was obtained by EPR spin trapping with 5,5-di-methylpyrroline-N-oxide. Fluorescence titration, DNA melting and linear dichroism studies of furocoumarins indicated that these compounds undergo efficient com-plexation and also intercalation into the DNA. The binding parameters K (intrinsic binding constant) and l/n (frequency of binding sites) of complexes between furocoumarin derivatives and DNA were determined to be in the range of 3900–23 900 M-^l and 0.017–0.045. The pho-toreaction of la’and lb’with 2′-deoxyguanosine (dGuo) afforded exclusively 7,8-dihydro-8-oxo-2′-deoxy-guanosine (8-oxodGuo), presumably through singlet oxygen, which was formed in a type II photooxidation process. In contrast, the hydroperoxide 2a oxidized dGuo to oxazo-lone as major and 8-oxodGuo as minor products through hydroxyl radicals, which were generated from 2a under photolytic conditions. Interestingly, the photoreactions of furocoumarins with salmon testes DNA showed that the highly reactive (φ= 0.85) hydroperoxide 2a is also most efficient in inducing the mutagenic DNA oxidation product 8-oxodGuo. Hence, the novel furocoumarin hydroperoxide 2a constitutes the first intercalating photo-Fen-ton reagent and serves as convenient hydroxyl radical source for genotoxicity studies.     

The determination of penicillins by titrations with mercury(II) solution.

A simple technique, involving two titrations with mercury(II) solutions, is described for the determination of penicillins and their degradation products. The first titration, at pH 4–5 on an untreated penicillin solution, gives the amount of degradation products; the second titration, on a hydrolysed solution at the same pH, gives the sum of the degradation products and penicillin degraded during the hydrolysis. Enzymic hydrolysis is superior to alkaline hydrolysis for penicillinase-sensitive penicillins. Enzyme-resistant penicillins should be hydrolysed with alkali at optimum conditions, e.g. for cloxacillin at pH 13.5 for 5 min. A standard deviation of less than 0.5 % was obtained for the penicillins investigated. The method is absolute; calibration with standard penicillin is not necessary.     

Radical intermediates induced by porphyrin triplets

In the photochemical reactions of triplets of both protoporphyrin-IX-dimethyl-ester (PP) and haematoporphyrin dihydrochloride (HP) with alpha-phenyl-ethyl hydroperoxide (HROOH) in C6H6 at room temperature, both O-O and C-C bonds are broken yielding alkoxy and carbon-centred radicals. The ruptures of C-C and O-H bonds were observed in the photochemical reaction of PP with tert-butanol in the same solvent, yielding alkoxy and carbon-centred radicals at lambda greater than or equal to 366 nm, while HP did not react photochemically with tert-butanol at lambda greater than or equal to 334 nm.     

Oxidation of ultra high molecular weight polyethylene (UHMWPE) part 1: Interpretation of the chemiluminescence curve recorded during thermal oxidation

The chemiluminescence curve of polyethylene differs from that of polypropylene even though the oxidation behaviour is similar. The CL curve of PE normally exhibits a double sigmoidal behaviour, whereas PP shows a single sigmoid, and its luminescence intensity is also much lower. It was found, by investigating the build-up of carbonyls and hydroperoxides by means of FTIR, that the first peak coincides with a maximum in hydroperoxide concentration and the second with the build-up of carbonyls. The intensity of the first peak is enhanced by doping the PE with DPA (9,10-diphenylanthracene), which is a chemiluminescence activator, but unaffected by doping the PE with DBA (9,10-dibromoanthracene), which is an energy acceptor. The intensity of the first peak also depends on the presence of carbonyls in the sample. From these observations it is concluded that the CL from PE is a type of activated chemiluminescence, which originates from hydroperoxide decomposition, with carbonyls acting as activator.     

Quantitation of lipid hydroperoxides using enhanced chemiluminescence

To determine lipid hydroperoxides, an analytical procedure was proposed based on enhanced chemiluminescence. The analytical system consisted of a lipid, Fe(II), and coumarin C-525, an enhancer of chemiluminescence. Lipid hydroperoxides were determined with spiked solutions using tert-butyl hydroperoxide as an internal standard. The analytical procedure provided a detection limit as low as 164 nM. Verification was performed by iodometric titration. The assay was used to determine total lipid hydroperoxides in food.     

A practical way of grafting maleic anhydride onto polypropylene providing high anhydride contents without sacrificing excessive molar mass

This study reports a reactive extrusion process leading to very high levels of anhydride grafting (2.5–3 wt %) along polypropylene backbone without recovering grafted PP waxes at the die exit. Such high graftings are attainable without excessive degradation of the PP chain by using a brominated reagent. Simultaneously, this brominated reagent allows the tuning of the grafted PP crystallinity via epimerization of the PP backbone. Indeed, the synthesis of a mainly isotactic/atactic stereoblock polymer containing high levels of grafted succinic anhydride moieties is demonstrated by NMR and melting enthalpies recorded by DSC are definitely observed depressed and broadened. Grafting levels of around 3 wt % have been achieved and ascertained by both chemical titration and NMR spectroscopy. In addition, FTIR spectroscopy reveals an unusual observation: for the first time, only one single pair of symmetric and asymmetric carbonyl stretching bands are observed on those grafted PP, while, in other processes of anhydride grafting, those symmetric and asymmetric bands were both split in at least two bands. This suggests, for the here reported process, the absence of interacting grafted anhydride rings, i.e., absence of closely grafted anhydride moieties and absence of poly(maleic anhydride). All those observations support that this “bromine route” brings a really new grafting process for PP. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2936–2947, 2008     

Thermolysis of polyethylene hydroperoxides in the melt, Part 12: Mechanisms and kinetics of thermolysis

The thermolysis of polyethylene hydroperoxides is attributed to the reaction of two hydroperoxide groups. This bimolecular reaction appears as a first-order reaction with the mean values of the hydroperoxide concentrations that can be used for the experimental verification of the kinetics. In low molecular mass liquids and solutions these findings would be irreconcilable. However, in polymer melts, this contradiction is more apparent than real. It is a consequence of the heterogeneous kinetics valid in polymer melts. The bimolecular reaction involves the decomposition of pairs of hydroperoxide groups that are relatively close in the elementary oxidation volumes. By diffusion these hydroperoxide groups can come close enough for reaction. From the chemical point of view the decomposition is a bimolecular reaction. However, from the kinetic point of view it is a first-order reaction of the hydroperoxide pairs. The dependency of the first-order rate on the initial hydroperoxide concentration is explained by the heterogeneous kinetics. The activation energy of the overall process can be related to the sum of the activation energies pertaining to the chemical reaction and to the diffusion process.     

Preparation of degradable polypropylene by an addition of poly(ethylene oxide) microcapsule containing TiO2

In order to prepare a novel photo-degradable polypropylene (PP), an addition of poly(ethylene oxide) (PEO) microcapsule containing TiO₂ to PP was performed. Adsorbed H₂O in the PEO phase and the TiO₂ photocatalytically reacted, and a hydroxyl radical (OH), which initiated the PEO degradation, was produced. The degraded PEO produced an acid and an aldehyde, which were able to facilitate PP degradation. The addition of the PEO/TiO₂ microcapsule brought about the facilitative effect of the PP degradation. In addition, an addition of a hindered amine light stabilizer (HALS) had a potential to suppress the PP degradation initiated by the microcapsule. The suppression effect was rising by the simultaneous addition of a phenolic antioxidant in the early phase of the PP degradation. However, the simultaneous addition showed an antagonism after 4 h degradation. This behavior suggested that the HALS also worked as a neutralizer of the produced acid.     

Use of 9,10-diphenylanthracene as a contrast agent in chemiluminescence imaging: The observation of spreading of oxidative degradation in thin polypropylene films

Thin films of polypropylene were doped with a chemiluminescence (CL) activator, 9,10-diphenylanthracene (DPA), and were thermally oxidised in a CL imaging apparatus to determine whether heterogeneous oxidation processes such as spreading of oxidation could be observed. The presence of DPA resulted in significantly more intense CL images compared with undoped polymer, due to the efficient chemically induced electron exchange luminescence reaction between DPA and hydroperoxides. Hence, the CL images from DPA-doped PP were used to locate the position of hydroperoxides in the oxidising polymer. For thermal oxidation at 150 and 140 °C hydroperoxides were observed to form in localised regions of the films, whilst other areas remained hydroperoxide free. As the oxidation time increased the concentration of hydroperoxides in these areas increased and they were observed to spread to the remainder of the polymer. Time-resolved line maps from the images indicated that zones with high concentration of hydroperoxides travel through the polymer during oxidation. Integrals of CL images from the thermal oxidation of DPA-doped polymers indicated that a significant degree of oxidation had occurred by the end of the “induction period” for a conventional CL-intensity oxidation-time profile. This is a likely reason why spreading of oxidation has not previously been observed for undoped PP films.