Long-term protecting group

Scheme 7.4 Examples of long-term protecting groups...

Wood preservatives are generally classified or grouped by the type of application or exposure environment in which they are expected to provide long term protection. Some preservatives have sufficient leach resistance and broad-spectrum efficacy to protect wood that is exposed directly to soil and water. These preservatives will also protect wood exposed above ground, and may be used in those applications with lower retentions (lower concentrations in the wood). Yet other preservatives have intermediate toxicity or leach resistance. This allows them to protect wood that is fully exposed to the weather, but not in contact with the ground. Other preservatives lack the permanence or toxicity to withstand continued exposure to precipitation, but... 

The fact that hydrolysis of the OTMS group is so facile makes it unsuitable for most alcohol moieties that require long-term protection. A more stable silyl derivative is the triethylsilyl group (O— SiEt3, O—TES). 

In terms of bond sets, the following sequence (Scheme 2.55) is equivalent to that of 1,3-dipolar cycloadditions. First an ynone is created by skeletal bond formation, and then a double Michael addition of two heteroatoms generates a 1,3-difunctionalized system, in which one of the functional groups is long-term protected. 

At the relatively low protection current density of 200 llA m and with the anode positioned on one side, it is to be expected that with this storage tank sufficient reduction in potential would be achieved on the other side of the tank from the anode. The off potential was measured using a measurement point at a depth of about 2 m as f/cu-cuso4 = -0.88 V at the tank. At the other side of the tank as well as above it, off potentials of-0.90 to -0.94 V were found. These potentials were measured with a protection current of 10 mA (anode 1 6 mA, anode 2 4 mA) with an additional resistance of 8 Q in the protection current circuit (see Fig. 11-2). With a direct connection between the tank and the group of magnesium anodes, the initial current was about 16 mA, which after 1 h of polarization decreased to about 14 mA. The reserve current, based on a long-term current of 10 mA, amounted to ca. 40% in the operation of the cathodic protection installation. 

---