Medium rings, definition

This is the synthesis of a somewhat controversial food preservative called BHT. It is an antioxidant that has been put in packaging to keep foods from becoming rancid from air oxidation. A balanced reaction would require two molecules of the alkene for each of the starting aromatic. The aromatic ring is relatively electron rich with two donors attached to it. With sulfuric acid present, the medium is definitely acidic. The first step is to generate the excellent electrophile needed for electrophilic aromatic substitution. For simplicity, let s symbolize sulfuric acid as H-A. The Markovnikov addition of a proton to isobutylene gives the tert-butyl carbocation, an excellent electrophile. 

The effective molarity (EM) is formally the concentration of the catalytic group (RCOO- in [5]) required to make the intermolecular reaction go at the observed rate of the intramolecular process. In practice many measured EM s represent physically unattainable concentrations, and the formal definition is probably relevant only in reactions (which will generally involve very large cyclic transition states) where the formation of the ring or cyclic transition state per se is enthalpically neutral, or in diffusion-controlled processes. For the formation of small and medium-sized rings and cyclic transition states the EM as defined above contains, and may indeed be dominated by, the enthalpy of formation of the cyclic form. This topic has been discussed briefly by Illuminati et al. (1977) and will be treated at greater length in a future volume in this series. 

Remind yourself of our definition of smalt, normal, medium, and large rings, and what ring strain means, by rereading p. 454, We will deal with what happens in large rings a. little later,... 

The Upase-catalyzed ROP of small-, medium- and large-ring lactones has often been reported. By definition. Upases hydrolyze triglycerides in an aqueous medium at one or more of the three ester bonds, and have been characterized by their drastically increased activity at the Hpid-water interface of a micellar or emulsified substrate. In a nonpolar medium, these enzymes are capable of initiating the ROP of cychc lactones, and this properly has been exploited for the synthesis of polyesters, especially from macrolides. 

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