Chlorosulfates

The temperature coefficients of the enthalpy of activation (AC;) for the hydrolysis of the three chlorosulfates, methyl, ethyl, and 8-chloro, are shown to have values of -50, -55, and -60 cal deg-' mol-'; values in the same range as previously reported for the hydrolysis of the sulfonyl chlorides. The corresponding value for the 8-methoxy isomer was -40 cal deg-' mol-', about the same as found for the p-methoxybenzenesulfonyl chloride. The kinetic solvent isotope effect, however, was significantly lower than reported for the sulfonyl chloride series, being about the same as found for the hydrolysis of the alkyl halides. While some degree of nucleophilic overlap is probably required in the activation process, the requirement here is reduced to about the same level as that for the primary halides, and there is no need to postulate a different mechanism on passing from the methyl to the ethyl member of the series, confirming the earlier conclusion of Buncel and Millington.On montre que les coefficients de temptrature de l'enthalpie d'activation (Ac: ) pour I'hydrolyse des trois chlorosulfates, mtthyle, Cthyle, et /I-chloro, ont les valeurs de -50, -55, et -60 cal deg-' mol-' ; valeurs se situant dans le mime domaine que celle rapporttes prtctdemment pour I'hydrolyse des chlorures de sulfonyl. La valeur correspondante pour I'isomtre /3-mtthoxy ttait de -40 cal deg-' mol-, environ la m&me que celle trouvte pour le chlorure de p-mtthoxybenztnesulfonyl. L'effet cinttique de solvant isotopique ttait toutefois largement plus faible que celui rapport6 pour la strie des chlorures de sulfonyl et ressemblait a celui qu'on avait trouvt pour I'hydrolyse des halogtnures d'alkyles. Alors que le proctdt d'activation demande un certain degrt de recouvrement nuclbophilique, le recouvrement dans le cas qui nous concerne est rtduit environ au mime niveau que dans le cas des halogtnures primaires, sans besoin de postuler un mtcanisme de passage difftrent du mtthyle a I'tthyle dans la strie, confirmant une conclusion prtcedente de Buncel et Millington.

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Mechanism for Hydrolysis of Primary Alkyl Chlorosulfates in Water. The Kinetic Solvent Isotope Effect and the Secondary Deuterium Isotope Effect

Ko¹,

Robertson²

1972

“…Orher Sj.sterns Since the entropy of activation criterion was first proposed as a result of our investigation of chlorosulfate sol~~olysis (7,8) several studies have appeared in the literature (35)(36)(37)(38)(39) relating to application of this mechanistic criterion to other systems. Of closest analogy are the studies with the structul.ally related chloroforrnates (36) and chlorosulfites (37).…”

Section: The Application O F the As* Frugt?let~tationmentioning

confidence: 99%

Solvent effect correlations and the mechanism of solvolysis of alkyl chlorosulfates

Buncel¹,

Millington²,

Wiltshire³

1977

. Can. J. Chem. 55. 1401 (1977).The rate of hydrolysis of the series of alkyl chlorosulfates ROS0,Cl (R = ethyl, n-propyl, isobutyl, neopentyl) has been measured as a function of solvent conlposition in dioxane-mater media. The solvent effect is examined from the viewpoint of dielectric constant, sol~ation number, and solvent ionizing power. The results point to a contirluous variation of solvolytic mechanisms (from S,2, through borderline, to S,1) along the series. The correlations are also considered with respect to the 'entropy criterion' for multiple bond scission previously advanced for solvolysis of the alkyl chlorosulfates. Solute-solvent interactions are identified as a possible alternative origin of the abnormally large AS" values observed in chlorosulfate solvolysis. Although many discussions of solvent effects o n reaction rates of nucleophilic substitution processes have been reported, systematic investigations of reaction series are relatively few in number (1-5). Previously we reported on the mechanism of solvolysis of a series of primary alkyl chlorosulfates, ROS02Cl, in aqueous dioxane (6-8). A normal mode of solvolysis, that is bimolecular or unilnolecular displacement o n carbon with -OS02Cl as the leaving group, was indicated by (i) the effect of nucleophiles on the rate of hydrolysis of rz-propyl chlorosulfate; (ii) the observation of a large lyate ion effect (ko,-lk,,, = 380) for n-propyl chlorosulfate but an absence of a lyate ion effect (ko,-lk,,, bimolecular mechanisms, respectively, with N u as the nucleophilic species). However, the observation of 'abnormally' large entropies of activation suggested that ternary fission (fragmentation (9)) -as occurring, i.e. transition states 3 and 4 with both carbon-oxygen and sulfur-chlorine bond weakenings.Further work has been undertaken in order lo obtain additional information on the nature of the solvolytic mechanism of alkyl chlorosulfates, and t o shed light on the validity of the entropy criterion of fragmentation. The present paper describes the results of the application of solvent Can. J. Chem. Downloaded from www.nrcresearchpress.com by 54.191.190.102 on 05/10/18For personal use only.

“…So far we have reported on the I neutral and alkaline methanolysis reactions (2) reactivity of the various species in this system. Some related compounds which have been examined from a similar point of view are the monoalkyl and aryl sulfates (3-7), the sulfites (8,9), and the halo sulfates (10)(11)(12).…”

mentioning

confidence: 99%

Bond Scission in Sulfur Compounds. Part X. The Hydrazinolysis of Methyl p-Nitrophenyl Sulfate

Buncel¹,

Chuaqui²

1975

ERWIN BUNCEL and CLAUDIO CHUAQUI. Can. J. Chem. 53, 1275Chem. 53, (1975. Reaction of methyl p-nitrophenyl sulfate with the hydrazine-hydrazine hydrochloride system in methanol gives rise to different types of behavior depending on the state of ionization of the reagent. For the H2NNH2/H2NNH3+ combination the observed reaction is conversion of methyl p-nitrophenyl sulfate to p-nitrophenyl sulfate ion (alkyl-oxygen scission). For the H2NNH3+/+H3NNH3+ combination, or with +H3NNH3+ alone, one observes the consecutive processes methyl p-nitrophenyl sulfate + p-nitrophenyl sulfate ion + p-nitrophenol (alkyl-oxygen followed by sulfur-oxygen scission). For the alkyl-oxygen scission process, i.e. nucleophilic displacement on the alkyl carbon, the observed pseudo first-order rate constant is given by the contributions of several nucleophilic species; k,,,. A method for the dissection of k,,, into the constituent terms is given. The sulfur-oxygen scission process is an acid catalyzed reaction and the measured kinetic data have been utilized for the derivation of the pK. of +H3NNH3+ in methanol. Rate data for the conversion of sodium p-nitrophenyl sulfate to p-nitrophenol in methanol containing HCI have also been determined in this connection.ERWIN BUNCEL et CLAUDIO CHUAQUI. Can. J. Chem. 53, 1275Chem. 53, (1975. La riaction du p-nitrophinyl sulfate de methyle avec le systime hydrazine -chlorhydrate d'hydrazine dans le mkthanol donne lieu a differents types de reaction dependant de I'Ctat d'ionisation du reactif. Pour la cornbinaison H2NNH2/H2NNH3 +, la reaction observte est la transformation du p-nitrophknyl sulfate de mkthyle en ion p-nitrophenyl sulfate (scission alkyle-oxygene). Pour la combinaison H 2 N N H 3 + / + H 3 N N H 3 + ou avec +H3NNH3+ seul, on observe des rkactions consecutives allant du p-nitrophknyl sulfate de methyle + I'ion p-nitrophknyl sulfate + p-nitrophenol (scission alkyle-oxygene suivie par une scission soufreoxygene). Pour le processus de scission alkyle-oxygene, i.e. le deplacement nuclCophile sur le carbone de la chaine alkyle, la constante de vitesse du pseudo premier ordre qui est observee est obtenue a partir des contributions de plusieurs espkes nucleophiles; k,,, = k,,, + kc,-IC1-1 + ~H~N N~~+ [ H~N N H~+ ] + ~H~N N H~[ H~N N H~] .Ondonne une methode pour ladissection du k,,, en ses termes constituants. Le processus de scission soufre-oxygene est une rkction acido catalyske et on a pu utiliser les valeurs cinetiques mesurkes pour dtterminer les valeurs de pK, du +H3NNH3+ dans le mkthanol. A cet effet on a aussi determine la vitesse de transformation (dans du methanol contenant du HCI) du p-nitrophknyl sulfate de sodium en p-nitrophenol.[Traduit par le journal]Methyl p-nitrophenyl sulfate is the first member of the family of mixed alkyl aryl sulfates to be subjected to intensive investigation. This particular substrate offers several possible electrophilic centers in its reactions with nucleophiles: the alkyl carbon, the sulfonyl sulfur, and the aryl carbon. So far we have reported on ...