The hydrolysis of the borohydride ion according to the equation (i) is catalysed by nickel-boron and cobalt-boron alloys. The metal-catalysed hydrolysis has been studied a t 22.0 "C by measurement of the hydrogen gas evolved.Arialysis of the gas evolved when the reaction is carried out in deuterium oxide shows that approximately half the hydrogen evolved originates from the borohydride and half from the solvent. The deuterium content of the gas increases with reaction time. In mixtures of H 2 0 and D20, preferential hydrogen evolution occurs and isotope separation factors of 8.5 (for a nickel-boron catalyst) and 9.2 (for a cobalt-boron catalyst) have been derived. BH,-+ 3H20 -W H2B0,-+ 4H2 (i)ALTHOUGH numerous studies have been made l4 of the solvolysis of the borohydride ion in aqueous solution, the metal-boron alloy-catalysed solvolysis has received relatively little a t t e n t i ~n . ~ Both the homogeneous acidcatalysed solvolysis and the heterogeneous alloy-cat alysed solvolysis follow the same stoicheiometry expressed by equation ( 1).BH,-+ 3H,O -w H,BO,-+ 4H, A study of the metal-boron alloy-catalysed solvolysis was undertaken as a part of a wider study concerned with the ' electroless ' or autocatalytic deposition of nickel and cobalt films. It is well-known that reaction (1) occurs concurrently with metal deposition when the borohydride ion is employed as reducing agent in such systems6 This work is also relevant to studies 7-9 of the anodic oxidation of the borohydride ion. EXPERIMENTAL AND RESULTSSolution Preparation.-Sodium borohydride (Koch-Light Pure ') was purified by recrystallisation from diglyme according to the method of Brown, Mead, and Subba Rao.10 The diglyme was first dried (CaC1,) and then distilled under nitrogen. The sodium borohydride produced by this method was determined by the method of Lyttle, Jensen, and Struck l1 to be 99.60,/,. Sodium hydroxide solutions were prepared from AnalaR sodium hydroxide and distilled water, and sodium deuteroxide solutions were prepared by dissolving sodium wire in deuterium oxide (99.6%) under nitrogen.Kinetic Studies.-Afiparatus.The apparatus consisted of a three-necked reaction vessel (25 ml) equipped with a nitrogen inlet and a thermometer. The third neck was connected through a water-condenser to a gas-burette to measure the volume of hydrogen evolved a t atmospheric pressure. The reaction vessel was immersed in a thermo-

Rate constants for the reactions of OH radicals and Cl atoms with 1-propanol (1-C 3 H 7 OH) have been determined over the temperature range 273-343 K by the use of a relative rate technique. The value of k(Cl + 1-C 3 H 7 OH) = (1.69 ± 0.19) × 10 −12 cm 3 molecule −1 s −1 at 298 K and shows a small increase of 10% between 273 and 342 K. The value of k(OH + 1-C 3 H 7 OH) increases by 14% between 273 and 343 K with a value of (5.50 ± 0.55) × 10 −12 cm 3 molecule −1 s −1 at 298 K, and further when combined with a single independent experimentally determined value at 753 K gives k(OH + 1-C 3 H 7 OH) = 4.69 × 10 −17 T 1.8 exp(422/T) cm 3 molecule −1 s −1 , which fits each data point to better than 2%. Two well-established structure-activity relationships for H abstraction by OH radicals give accurate predictions of the rate constant for OH + 1-C 3 H 7 OH, provided the β-CH 2 group is given an increased reactivity of a factor of about 2 over that for the structurally equivalent CH 2 group in alkanes at 298 K. REACTIONS OF HYDROXYL RADICALS AND CHLORINE ATOMS WITH 1-PROPANOL 111A quantitative product analysis was carried out at 298 K for the Cl-initiated photooxidation of 1-C 3 H 7 OH, using both FTIR and gas chromatography. HCHO, CH 3 CHO, and C 2 H 5 CHO were the only major organic primary products observed, although HCOOH was found in much smaller amounts as a secondary product. A key characteristic of the analysis was that the initial values of the product ratio [CH 3 CHO]/[C 2 H 5 CHO] were effectively constant for NO pressures between 0.15 and 0.3 Torr, but fell by about 35% as the pressure fell to 0.0375 Torr. From a detailed consideration of the mechanism for the oxidation, it is suggested that C 2 H 5 CHO, CH 3 CHO (+HCHO), and 3 molecules of HCHO are formed uniquely from CH 3 CH 2 CHOH, CH 3 CHCH 2 OH, and CH 2 CH 2 CH 2 OH radicals, respectively. On this basis, use of the product yields gives the branching ratios of 56, 30, and 14% for Cl atom reaction at the α-, β-, and γ-C H positions in 1-C 3 H 7 OH at 298 K. Given the very low temperature coefficients involved, little change will occur over tropospheric temperature ranges.

The pyrolysis of 1.2-dichloroethane in a static system has been studied by g.1.c. analysis of the products and by pressure measurements in the temperature range 340-51 5 "C, surface :volume ratio range (1 -32-37.4) cm-l, and with initial pressures from 0.3 to 300 Torr, in reaction vessels coated with pyrolytic carbon films.The major reaction is dehydrochlorination to vinyl chloride, but ethylene is also a primary reaction product. The ethylene yield is very small (<2% of the vinyl chloride) under conditions of low surface:volume ratio. It is concluded that the ethylene is produced by a concurrent heterogeneous dechlorination of 1.2-dichloroethane.At low surface :volume ratio the vinyl chloride produced is closely paralleled by the pressure increase and the reaction is found to have a high order (2.4-2.8) and activation energy (73 k 3 kcal mol-l). The reaction is inhibited by additions of vinyl chloride, ethylene, and propene, and accelerated by added hydrogen chloride, oxygen, and chlorine. The radical-chain mechanism previously suggested by Barton and Howlett is discussed and modified to account for the experimental observations. The pressure-time curves obtained from experiments at high surface :volume ratio indicate that under these conditions the reaction is autocatalytic. The maximum rate corresponds to an order of 1.5 and an activation energy of 33.0 kcal mol-I. It is suggested that the autocatalysis is due to a heterogeneous initiation process involving adsorbed chlorine.THE pyrolysis of 1,2-dichloroethane has previously been studied under homogeneous and heterogeneous 5-7 conditions. Under static conditions it is widely accepted that the reaction is homogeneous and of the first order and shows many characteristics of a chain reaction, such as inhibition by propene, acceleration by oxygen and chlorine, and the presence of induction periods. To account for these features, Howlett suggested the mechanism of reactions ( 1)-( 4).In order to fit the(3)observed overall rate expression, i.e., equation (5), it was necessary to assume an unreasonably low pre-k1s-l = 1010.81exp (-47,00O/RT) (5) exponential factor of 1O1O s-l for reaction (3). The corollary of a long-lived C,H3C1, radical proved to be a convenient explanation for the observed induction periods, which were attributed to the slow build-up of this radical to its stationary-state concentration.Both Barton and Howlett (who used vessels with s/v 2.7 and 8.5 cm-l) and Howlett (who varied s/v from 2.2 to 22) found the rate of reaction to be little affected by packing the reaction vessel. Accordingly, Howlett suggested that steps (1) and (4) as well as ( 2) and (3) were homogeneous.Kapralova and Semenov4 have since shown, using differential calorimetry and large reaction vessels, that the reaction is isolated in a zone near the vessel walls. This implies that the reaction is initiated and in part terminated a t the vessel walls.

No abstract

to be ca. 1000 times lower than the average tropospheric OH radical concentrations [5]. The amount of data concerning the reactions of ethers and other oxygenated compounds with Cl atoms [1,6 -12] is not as extensive as that for the reaction with OH radicals and is increased by this study.By measurement of the rate constants for the reactions of methylethylether with OH radicals and Cl atoms the tropospheric lifetimes with respect to removal by each of these species can be estimated. Such information is important when calculating the ozone forming potential [13] of volatile organic compounds and thus assessing their contribution to atmospheric pollution.A relative rate technique has been used to obtain rate constants for the reactions of OH radicals and Cl INTRODUCTIONIn addition to being used as solvents, ethers are being added [1,2] to unleaded petrol in order to increase the octane rating and reduce the amounts of unburnt hydrocarbons, carbon monoxide, and other noxious emissions from exhausts. Ethers are mostly removed in the troposphere by their reaction with hydroxyl radicals, although chlorine atoms have recently been considered as potential tropospheric oxidants [3] ABSTRACT: The rate constants for the gas-phase reactions between methylethylether and hydroxyl radicals (OH) and methylethylether and chlorine atoms (Cl) have been determined over the temperature range 274 -345 K using a relative rate technique. In this range the rate constants vary little with temperature and average values of k MEEϩOH ϭ (6.60 Ϫ2.62 ϩ3.88 ) ϫ 10 Ϫ12 cm 3 molecule Ϫ1 s Ϫ1 and k MEEϩCl ϭ (34.9 Ϯ 6.7) ϫ 10 Ϫ11 cm 3 molecule Ϫ1 s Ϫ1 were obtained. The atmospheric lifetimes of methylethylether have been estimated with respect to removal by OH radicals and Cl atoms to be ca. 2 days and ca. 30 -40 days, respectively.