Alicyclic Carboxylic Acids Research Articles

Biochar/iron oxide composite as an efficient peroxymonosulfate catalyst for the degradation of model naphthenic acids compounds

Naphthenic acids (NAs) are a mixture of aliphatic and alicyclic carboxylic acids which are persistent in the environment. In this study, a sludge-based biochar/iron oxide (B-FeOx) catalyst with 3D flower-like shaped structure was prepared through a facile hydrothermal method. For the first time, the B-FeOx catalyst was employed to activate peroxymonosulfate (PMS) for the removal of two model NA compounds (1-adamantanecarboxylic acid (ACA) and 4-methylheptanoic acid) at pH 8.50. Compared to biochar or FeOx alone, a higher degradation efficiency (96.1%) and faster degradation rate (k = 0.100 min−1) of ACA were obtained by the B-FeOx composite at a catalyst dose of 2.0 g/L and PMS dose of 2.5 mM. The higher degradation efficiency of B-FeOx was attributed to the improved surface area and pore volume as well as the abundant reactive sites induced by the flower-like structure. Furthermore, the hydroxyl radical (•OH) generated in the B-FeOx/PMS system was the dominant radical for both ACA and 4-methylheptanoic acid degradation as demonstrated through radical quenching experiments. The presence of chloride ions in the B-FeOx/PMS system showed a suppression effect on the degradation of ACA and 4-methylheptanoic acid at Cl− concentrations between 5 and 20 mM. No significant difference in the degradation rates of ACA and 4-methylheptanoic acid was observed at different Cl− concentrations. Overall, the results of this study showed that the sludge (waste material)-based B-FeOx composite may have the potential to be utilized as PMS catalyst for the removal of NAs that are especially abundant in oil sands process water.

Alicyclic carboxylic acids in soil humic acid as detected with ultrahigh resolution mass spectrometry and multi-dimensional NMR

It has been well accepted that humic acids in soils comprise both aromatic and aliphatic structural units that harbor mainly oxygenated functional groups such as carboxylic acids, aldehydes, ketones, and hydroxyl groups. Recent mass spectral data obtained from electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) suggest that the main functional groups in humic acids are carboxylic acids bound to both alicyclic and condensed aromatic molecules. It was suggested that these structural entities originate from oxidation of lignin. To provide additional support, detailed structural characteristics were obtained here using several multi-dimensional nuclear magnetic resonance (NMR) techniques to observe the molecular connectivity of humic acid components, with a focus on carboxylic acids in particular. The humic acid sample examined had been shown to exhibit structural characteristics similar to a larger set of soil humic acids. In this study, many carboxylic acid resonances were found to correlate with protons that could be assigned to aliphatic and alicyclic chemical shift regions. Functional groups with heteroatoms such as alcohols, some olefins and an assortment of methyl groups were found to correlate within 2–3 bonds of carboxylic acid groups. The collection of structural components and their proximity to a variety of carboxylic groups supports the occurrence of carboxylated alicyclic molecules as important elements of the aliphatic portion of soil humic acids and a pathway from lignin is consistent with recent findings.

Standard method design considerations for semi-quantification of total naphthenic acids in oil sands process affected water by mass spectrometry: A review

Naphthenic acids are a complex class of thousands of naturally occurring aliphatic and alicyclic carboxylic acids found in oil sands bitumen and in the wastewater generated from bitumen processing. Dozens of analytical methods have been developed for the semiquantification of total naphthenic acids in water samples. However, different methods can give different results, prompting investigation into the comparability of the many methods. A review of important methodological features for analyzing total naphthenic acids is presented and informs the design of future standard methods for the semiquantification of total naphthenic acids using mass spectrometry. The design considerations presented are a synthesis of discussions from an Environment and Climate Change Canada (ECCC) led taskforce of 10 laboratory experts from government, industry and academia during April 2016 and subsequent discussions between University of British Columbia and ECCC representatives. Matters considered are: extraction method, solvent, pH, and temperature; analysis instrumentation and resolution; choice of calibration standards; use of surrogate and internal standards; and use of online or offline separation prior to analysis. The design considerations are amenable to both time-of-flight and Orbitrap mass spectrometers.

Comprehensive structure-selective characterization of dissolved organic matter by reducing molecular complexity and increasing analytical dimensions

Deciphering the molecular codes of dissolved organic matter (DOM) improves our understanding of its role in the global element cycles and its active involvement in ecosystem services. This study demonstrates comprehensive characterization of DOM by an initial polarity-based stepwise solid phase extraction (SPE) with single methanol elution of the cartridges, but separate collection of equal aliquots of eluate. The reduction of molecular complexity in the individual DOM fractions attenuates intermolecular interactions and substantially increases the disposable resolution of any structure selective characterization. Suwannee River DOM (SR DOM) was used to collect five distinct SPE fractions with overall 91% DOC recovery. Optical spectroscopy (UV and fluorescence spectroscopy), high-field Fourier transform ion cyclotron mass spectrometry (FTICR MS) and nuclear magnetic resonance (NMR) spectroscopy showed analogous hierarchical clustering among the five eluates corroborating the robustness of this approach. Two abundant moderately hydrophobic fractions contained most of the SR DOM compounds, with substantial proportions of aliphatics, carboxylic-rich alicyclic molecules, carbohydrates and aromatics. A minor early eluting hydrophilic fraction was highly aliphatic and presented a large diversity of alicyclic carboxylic acids, whereas the two late eluting, minor hydrophobic fractions appeared as a largely defunctionalized mixture of aliphatic molecules. Comparative mass analysis showed that fractionation of SR DOM was governed by multiple molecular interactions depending on O/C ratio, molecular weight and aromaticity. The traditional optical indices SUVA254 and fluorescence index (FI) indicated the relative aromaticity in agreement with FTICR mass and NMR spectra; the classical fluorescent peaks A and C were observed in all four latter eluates. This versatile approach can be easily expanded to preparative scale under field conditions, and transferred to different DOM sources and SPE conditions.

Synthesis and structure-properties relationship studies of biodegradable hydroxylammonium-based protic ionic liquids

In this work sixteen hydroxyl ammonium Protic Ionic Liquids derived from a proton transfer reaction between four different substituted amines and four different low molecular weight aliphatic and alicyclic carboxylic acids have been synthesized. The synthesized PILs were structurally characterized by NMR and FT-IR spectroscopy whereas two of their more important physicochemical properties namely viscosity and glass transition temperature (Tg) were evaluated. The effect of alkyl chain length and substitution on the anionic and cationic component of the PILs scaffold has been discussed for the studied properties. It seems that Tg values are mainly affected by the carboxylate anion structure whereas viscosity is controlled mainly by the structural features of the cationic part of the PILs. In order to estimate their environmental impact and reinforce their “green” character, biodegradation studies, as well as toxicity evaluation experiments have also been conducted. The synthesized PILs can be confidently labelled as green considering that they are not toxic or present low toxicity to the nauplii of the brine shrimp A. salina whereas they show biodegradability levels between 41–64%, according to the manometric respirometric method which measures the biological oxygen demand (BOD5) by microorganisms in order to degrade PILs via bio-oxidation in five days.

Development of a rapid liquid chromatography tandem mass spectrometry method for screening of trace naphthenic acids in aqueous environments

Over the past 20 years, oil sands exploration and processing in Canada have grown steadily, leading to the development of intensive large-scale operations in Alberta, Canada. Naphthenic acids (NAs), a complex mixture of aliphatic and alicyclic carboxylic acids, are by-products of oil sands processing and are known to be toxic. While oil sands processing water (OSPW) is contained in tailings ponds, potential seepage and leaking of OSPW and its contaminants into surrounding surface water systems is a concern. The ability to quantify NAs and their isomers in OSPW surrounding water is essential for monitoring these spills. Unfortunately, quantification of NAs and their isomers is challenging due to the complexity of the NA mixtures, the lack of commercially available standards, and interference from naturally occurring NA compounds. Techniques such as FT-IR and GC/MS are currently used to analyse NAs, but are limited by poor sensitivity and specificity in the case of FT-IR and long sample preparation and instrument run time for GC/MS. To tackle these issues, a rapid LC/MS method was developed which can quickly quantify NAs in surface water with much better sensitivity and specificity than current methods. This method uses large volume injection, ESI negative mode and a Poroshell LC column to improve the method limits of detection (LOD) and quantitation (LOQ). The method is robust and has no complicated sample preparation steps. The method detection limit (MDL) is 0.01mg/L (10ppb) and low limit of quantitation (LLOQ) of 0.1mg/L (100ppb), both for surface water. The developed method was tested with samples from the oil sands producing region, and demonstrated its applicability for fast screening of surface water samples before resorting to costly high accuracy and high resolution mass spectrometry determination. This is the first very rapid LC/MS method using large volume single column direct injection for quantitative determination of naphthenic acids in surface water.

Electrospray ionization mass spectrometry studies of cyclodextrin‐carboxylate ion inclusion complexes

Aqueous solutions containing simple model aliphatic and alicyclic carboxylic acids (surrogates 1-4) were studied using negative ion electrospray mass spectrometry (ESI-MS) in the presence and absence of alpha-, beta-, and gamma-cyclodextrin. Molecular ions were detected corresponding to the parent carboxylic acids and complexed forms of the carboxylic acids; the latter corresponding to non-covalent inclusion complexes formed between carboxylic acid and cyclodextrin compounds (e.g., beta-CD, alpha-CD, and gamma-CD). The formation of 1:1 non-covalent inclusion cyclodextrin-carboxylic complexes and non-inclusion forms of the cellobiose-carboxylic acid compounds was also observed.Aqueous solutions of Syncrude-derived mixtures of aliphatic and alicyclic carboxylic acids (i.e. naphthenic acids; NAs) were similarly studied using ESI-MS, as outlined above. Molecular ions corresponding to the formation of CD-NAs inclusion complexes were observed whereas 1:1 non-inclusion forms of the cellobiose-NAs complexes were not detected. The ESI-MS results provide evidence for some measure of inclusion selectivity according to the 'size-fit' of the host and guest molecules (according to carbon number) and the hydrogen deficiency (z-series) of the naphthenic acid compounds. The relative abundances of the molecular ions of the CD-carboxylate anion adducts provide strong support for differing complex stability in aqueous solution. In general, the 1:1 complex stability according to hydrogen deficiency (z-series) of naphthenic acids may be attributed to the nature of the cavity size of the cyclodextrin host compounds and the relative lipophilicity of the guest.

Naphthenic acids as indicators of crude oil biodegradation in soil, based on semi‐quantitative electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Crude oil contaminated soil cores were collected from a basin that contained oily solids left from three decades of oil production. Hydrocarbon biomarker analyses revealed that the soil extracts were moderately biodegraded compared with the non-degraded source oil. The degree of biodegradation also decreased with core depth (7 cm to 1 m). These data were correlated to compositional changes observed in acidic NSO-compounds that were selectively ionized and mass resolved by negative ion electrospray Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). Among the NSO-compounds ionized, the increase in naphthenic acid concentration (e.g., acyclic and alicyclic carboxylic acids) best correlated with the increase in biodegradation (e.g., from non-degraded to moderately degraded) as determined by the hydrocarbon biomarker analyses. The most biodegraded surface extracts (7 cm) exhibited an 80% increase in the abundance of acids relative to the source oil. Use of an internal standard allowed the semi-quantitative determination of the total naphthenic acid concentration, which decreased significantly (P < 0.05) with soil depth. Furthermore, the shift to higher double bond equivalents (DBEs), from acyclic to alicyclic acids, indicated that the increase in acids in the soil extracts was predominantly due to biotic processes. This work demonstrates the potential of ESI FT-ICR MS as a semi-quantitative tool to monitor the production of naphthenic acids during crude oil biotransformation in the environment.

Comparison of high‐ and low‐resolution electrospray ionization mass spectrometry for the analysis of naphthenic acid mixtures in oil sands process water

The oil sands regions of Northern Alberta, Canada, contain an estimated 1.7 trillion barrels of oil in the form of bitumen, representing the second largest deposit of crude oil in the world. A rapidly expanding industry extracts surface-mined bitumen using alkaline hot water, resulting in large volumes of oil sands process water (OSPW) that must be contained on site due to toxicity. The toxicity has largely been attributed to naphthenic acids (NAs), a complex mixture of naturally occurring aliphatic and (poly-)alicyclic carboxylic acids. Research has increasingly focused on the environmental fate and remediation of OSPW NAs, but an understanding of these processes necessitates an analytical method that can accurately characterize and quantify NA mixtures. Here we report results of an interlaboratory comparison for the analysis of pure commercial NAs and environmental OSPW NAs using direct injection electrospray ionization mass spectrometry (ESI-MS) and high-pressure liquid chromatography/high-resolution mass spectrometry (HPLC/HRMS). Both methods provided very similar characterization of pure commercial NA mixture; however, the m/z selectivity of HPLC/HRMS was essential to prevent substantial false-positive detections and misclassifications in OSPW NA mixtures. For a range of concentrations encompassing those found in OSPW (10-100 mg/L), both methods produced linear response, although concentrations of commercial NAs above 50 mg/L resulted in slight non-linearity by HPLC/HRMS. A three-fold lower response factor for total OSPW NAs by HPLC/HRMS was largely attributable to other organic compounds in the OSPW, including hydroxylated NAs, which may explain the substantial misclassification by ESI-MS. For the quantitative analysis of unknown OSPW samples, both methods yielded total NA concentrations that correlated with results from Fourier transform infrared (FTIR), but the coefficients of determination were not high. Quantification by either MS method should therefore be considered semi-quantitative at best, albeit either method has substantial value in environmental fate experiments where relative concentration changes are the desired endpoints rather than absolute concentrations.

Ozonation of oil sands process water removes naphthenic acids and toxicity

Naphthenic acids are naturally-occurring, aliphatic or alicyclic carboxylic acids found in petroleum. Water used to extract bitumen from the Athabasca oil sands becomes toxic to various organisms due to the presence of naphthenic acids released from the bitumen. Natural biodegradation was expected to be the most cost-effective method for reducing the toxicity of the oil sands process water (OSPW). However, naphthenic acids are poorly biodegraded in the holding ponds located on properties leased by the oil sands companies. In the present study, chemical oxidation using ozone was investigated as an option for mitigation of this toxicity. Ozonation of sediment-free OSPW was conducted using proprietary technology manufactured by Seair Diffusion Systems Inc. Ozonation for 50 min generated a non-toxic effluent (based on the Microtox bioassay) and decreased the naphthenic acids concentration by ∼70%. After 130 min of ozonation, the residual naphthenic acids concentration was 2 mg l −1: <5% of the initial concentration in the filtered OSPW. Total organic carbon did not change with 130 min of ozonation, whereas chemical oxygen demand decreased by ∼50% and 5-d biochemical oxygen demand increased from an initial value of 2 mg l −1 to a final value of 15 mg l −1. GC–MS analysis showed that ozonation resulted in an overall decrease in the proportion of high molecular weight naphthenic acids ( n ⩾ 22).

Capillary HPLC/QTOF-MS for Characterizing Complex Naphthenic Acid Mixtures and Their Microbial Transformation.

A rapidly expanding oil sands industry in Canada produces and indefinitely stores large volumes of toxic aqueous tailings containing high concentrations of naphthenic acids (NAs), a complex mixture of naturally occurring aliphatic or alicyclic carboxylic acids. Although there is an acknowledged need to reduce the environmental risks posed by NAs, little is understood about their environmental fate due to a lack of appropriate analytical methods. A dilute-and-shoot reversed-phase capillary HPLC/QTOF-MS method was developed that combines high specificity and sensitivity, quantitative capabilities, the ability to detect novel transformation products, and new structural information within each NA isomer class. HPLC separated NAs, based on carbon number, degree of cyclization, and the extent of alkyl branching, and in so doing increased analytical sensitivity up to 350-fold while providing additional specificity compared to infusion techniques. For tailings water, an interlaboratory study revealed many differences in isomer class profiles compared to an established GC/MS method, much of which was attributed to the misclassification of oxidized NAs (i.e., NA + O) by low-resolution GC/MS. HPLC/QTOF-MS enabled the detection of oxidized products in the same chromatographic run, and Van Krevelen diagrams were adapted to visualize the complex data. A marked decrease of retention times was evident in Syncrude tailings water compared to a commercial mixture, suggesting that tailings water is dominated by highly persistent alkyl-substituted isomers. A biodegradation study revealed that tailings water microorganisms preferentially deplete the least alkyl-substituted fraction and may be responsible for the NA profile in aged tailings water.

Starter Unit Specificity of the Asukamycin “Upper” Chain Polyketide Synthase and the Branched-Chain Fatty Acid Synthase of Streptomyces nodosus subsp. asukaensis

Asukamycin, a member of the manumycin family of antibiotics, obtained from Streptomyces nodosus subsp. asukaensis, contains two amide-linked polyketide chains, one of which, the upper chain, is initiated by cyclohexanecarboxylic acid as the starter unit. Analysis of the congeners of asukamycin present in the fermentation and of the fatty acid spectrum of the mycelial lipids revealed that the upper chain polyketide synthase (PKS) and the branched-chain fatty acid synthase (FAS) of S. nodosus ssp. asukaensis share qualitatively, although not quantitatively, the same starter unit selectivity for branched chain and alicyclic carboxylic acids. Feeding of various alicyclic carboxylic acids of different ring size resulted in the formation of new asukamycin analogs as well as changes in the fatty acid spectrum. Feeding of various alicyclic carboxylic acids also shut off the endogenous production of cyclohexanecarboxylic acid.

Is Biodegradation of Bitumen a Source of Recalcitrant Naphthenic Acid Mixtures in Oil Sands Tailing Pond Waters?

Carboxylic acids are transient metabolites during the mineralization of petroleum hydrocarbons. Crude oils, however, vary in their proportion of the hydrocarbon components. Depending on structure, some carboxylic acid metabolites resist further biodegradation and persist in aquatic systems. During the extraction of oil sands bitumen, recalcitrant carboxylic acid mixtures, collectively referred to as naphthenic acids (NAs), are released into the wastewaters. These waters also contain unrecovered bitumen from the oil sands. The unextracted bitumen is often overlooked as a possible source of the petroleum acids. The present article discusses the literature data on the biotransformation of hydrocarbons in bitumen from oil sands to the corresponding petroleum carboxylic acids. Some insight is given on the mechanism of the biodegradation process. The susceptibility to biodegradation is affected by differences in alicyclic carboxylic acids such as carbon chain length, chain branching, and the oddness or evenness of carbon chain containing the carboxylic group, positions where alkyl groups are substituted on the cyclic ring, geometrical isomerism, and number of cyclic rings.

Photolysis of Naphthenic Acids in Natural Surface Water

Naphthenic acids are toxic and corrosive substances in oil sands leachates comprising a group of saturated aliphatic and alicyclic carboxylic acids in hydrocarbon deposits (petroleum, oil sands bitumen, and crude oils). In the current study, photolysis was applied to naphthenic acid mixtures and individual compounds to determine the efficacy of a variety of UV/vis radiation sources for reducing both concentration and aryl hydrocarbon (Ah) receptor binding as a measure of toxicity. The results show that the concentrations of neither the compounds nor the mixtures were significantly reduced in Athabasca River water, although compositional changes occurred within the mixtures and Ah receptor binding potential was affected by photolysis. Photolysis at UV254 was the most effective radiation source applied in all instances.

A Review of the Occurrence and Fate of Naphthenic Acids in Aquatic Environments

Naphthenic acids are comprised of a large collection of saturated aliphatic and alicyclic carboxylic acids found in hydrocarbon deposits (petroleum, oil sands bitumen, and crude oils). Naphthenic acids enter surface water systems primarily through effluent discharge, but also through groundwater mixing and erosion of riverbank oil deposits. Of the possible environmental receptors (i.e., air, soil, and water), the most significant is water. Ambient levels of naphthenic acids in northern Alberta rivers in the Athabasca Oil Sands are generally below 1 mg L−1. However, tailings pond waters may contain as high as 110 mg L−1. The complexity of natural naphthenic acids in petroleum deposits poses an analytical challenge as reflected by the several techniques reported for quantitation of naphthenic acids in the environment. Although naphthenic acids are known to be persistent biomarkers used in identification of oil source maturation, little is established regarding their relative degradation pathways in aquatic environments. Published research related to the potential for microbiological degradation and adsorption to typical Athabasca Oil Sands soils reveal that naphthenic acids are likely to persist in the water column and, with prolonged exposure, accumulate in sediments. However, other than a very general knowledge of environmental persistence, the occurrence and fate of naphthenic acids has been sparsely studied. This article brings together some of those environmental persistence results, as well as detailed information regarding the origin of naphthenic acids in tailings ponds, chemistry and toxicological considerations, current analytical methods for aquatic sampling, and areas of future remediation research.

Determination of Dissolved Naphthenic Acids in Natural Waters by Using Negative-Ion Electrospray Mass Spectrometry

Naphthenic acids (NAs) have been implicated as some of the most toxic substances in oil sands leachates and identified as priority substances impacting on aquatic environments. As a group of compounds, NAs are not well characterized and comprise a large group of saturated aliphatic and alicyclic carboxylic acids found in hydrocarbon deposits (petroleum, oil sands bitumen, and crude oils). Described is an analytical method using negative-ion electrospray ionization mass spectrometry (ES/MS) of extracts. Preconcentration was achieved by using a solid-phase extraction procedure utilizing a crosslinked polystyrene-based polymer with acetonitrile elution. Recovery of the Fluka Chemicals NA mixture was highly pH-dependent, with 100% recovery at pH 3.0, but only 66 and 51% recoveries at pHs 7 and 9, respectively. The dissolved phase of the NA was very dependent on sample pH. It is thus critical to measure the pH and determine the appropriate mass profiles to identify NAs in natural waters. The ES/MS analytical procedure proved to be a fast and sensitive method for the recovery and detection of NAs in natural waters, with a detection limit of 0.01 mg/L.

Preparation of (1S)-verbenone, aromatic and alicyclic carboxylic acids by oxidation of aldehydes, primary and secondary alcohols with Nocardia corallina

(lS)-Verbenone, (S)-perillyl acid, cinnamic acid, meta-nitrocinnamic acid, veratric acid and 2-naphthoic acid were prepared, at 1 mM scale, from the corresponding alcohols or aldehydes with whole cells of Nocardia corallina B-276, in yields from 19 to 71% (w/w). Similar microbiological oxidations gave poor yields with the heterocyclic alcohols: 3-pyridylmethanol, 4-flavanol and 4-chromanol.

Naphthenic acids as antiwear additives for jet fuels

One of the ways in which the antiwear properties of jet fuels can be improved is the use of lubricity agents, otherwise known as antiwear additives. Among the various compounds that have antiwear properties in these fuels, naphthenic, acids merit special attention. These are alicyclic carboxylic acids, in most cases monobasic, with five- and six-membered carbon rings; they have the general formula R(CH{sub 2}){sub n}COOH, where R is a naphthene radical. Natural naphthenic acids consist mainly of acids of the cyclopentane series, beginning with the simplest, in particular cyclopentylacetic acid. The lower naphthenic acids are monocyclic; the higher acids, beginning with C{sub 13}, are bicyclic and polycyclic. Naphthenic acids of the cyclohexane series are encountered less frequently; they may be found, for example, in Baku, California, and Sakhalin crudes. The most widely used method for obtaining naphthenic acids is the treatment of light distillates, lube distillates, and diesel fuels. The standard GOST 13302-77 establishes several grades of naphthenic acids, depending on the raw material and the production technology. This work was aimed at the utilization of wastes containing naphthenic acids, with subsequent use as jet fuel additives.

Proton affinity determinations using the kinetic method in an ion trap mass spectrometer

Proton affinities for various compounds have been estimated using a quadrupole ion trap by generating and mass-selecting proton-bound dimers and measuring their dissociation kinetics (A–H + −B → AH + + B and/or BH + + A). From the relative abundances of the fragment ions ([BH +] and [AH +]), which are related to their relative proton affinities by ln ([AH +]/[BH +]) = ΔPA/ RT, it is shown that the proton affinities of the alicyclic carboxylic acids decrease in the order: cyclohexane- > cyclopropane- > cyclopentane- > cyclobutanecarboxylic acid. Proton affinity values for these species, measured from their proton-bound dimers with specific ketones, esters and carboxylic acids of known PA, are determined to be 198.3 ± 0.2 kcal mol −1, 198.0 ± 0.2 kcal mol −1, 197.8 ± 0.2 kcal mol −1 and 197.0 ± 0.2 kcal mol −1, respectively. The major contribution to the estimated uncertainties in these values results from the uncertainties in literature proton affinity values for the reference compounds. Proton affinity differences of ≤ 0.1 kcal mol −1 are measurable and differences as small as 0.04 ± 0.02 kcal mol −1 are estimated to be detectable. Similarly, the proton affinities for o-, m- and p-methylbenzoic acid are determined to be 201.3 ± 0.2, 200.0 ± 0.2, 201.4 ± 0.2 kcal mol −1, respectively. The ability to measure such small PA differences is believed to be a consequence of the low internal energy of the activated proton-bound dimers. The kinetic method has also been used to examine the effect of deuterium labeling on proton affinity. Secondary isotope effects on proton affinity are examined for both meta and para deuterated benzoic acid proton-bound to benzoic acid ( k H/ k D = 1.0 ± 0.1 and 0.9 ± 0.1, respectively), for acetophenone proton-bound to deuterated-acetophenone (C 6H 5C(O)CD 3) ( k H/ k D = 0.7 ± 0.1) and for 2-pentanone proton-bound to deuterated 2-pentanone (CH 3CH 2CH 2C(O)CH 3) ( k H/ k D = 2.1 ± 0.2). These results, as well as those for the carboxylic acids and benzoic acids given above, are accounted for in terms of stabilizing electronic effects in the protonated molecules.

The invention of radical chain reactions: Part XIV. A decarboxylative radical addition to quinones

Irradiation of esters 3 derived from aliphatic or alicyclic carboxylic acids and N-hydroxy-2-thiopyridone in the presence of various quinones gives high yields of the corresponding adducts (e.g. 9 ) with net loss of carbon dioxide.