Synthesis from traces

A trace is a sequence of instructions executed by a program on some given input data. Traces are often used by human beings to explain an existing algorithm. For instance, the protocol of using a telephone is easily described by sample traces. 

Traces are however a very tedious and error-prone specification formalism. Worse, traces oblige the specifier to already know the desired algorithm, which often goes counter the setting of algorithm synthesis. All this somewhat discredits synthesis from traces as an approach to automatic programming, but see below. 

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Biermann has applied this two-step approach, but he used his own synthesis from traces mechanism [Biermann 72] for the second step. The resulting synthesis mechanism for so-called regular LISP programs (with only one parameter, and where the only predicate, if any, is atom) is described by [Biermann 78,84a]. Let s first illustrate it on a simple synthesis (taken from [Biermann 92]). 

Second, the synthesis from traces mechanism proceeds by merging the obtained functions into a minimal number of functions that preserve the original computations. If a merged function is multiply defined, then a predicate generator searches for discriminants. This works here as follows. The functions/i,/4,/5,/g,/9 may be merged into a function reverse. The predicate generator infers that the body of /4,/g,/9 is applicable iff the parameter is an atom. Hence the following definition of reverse ... 

When the fluorine used for synthesis contained traces of oxygen, the solid behaved as a powerful oxidant (causing 2-propanol to ignite on contact) and it also exploded on impact. Material prepared from oxygen-free fluorine did not show these properties, which were ascribed to the presence of traces of dioxy geny 1 tetrafluoroborate (above). 

Tetrabromobenzene used from sources other than Lancaster Synthesis contained trace amounts of an impurity that carried through the entire reaction scheme. This impurity gave a proton resonance at 1.58 ppm in the starting... 

Previous synthesis of (+ )-marasin using reagent 13 led to difficulties in the separation of (+ )-maiasin from traces of (—)-menthoi in the product (53). 

Potassium iodide is not easily purified by the usual methods of recrystallization because of the great solubility of the salt and because of the doubtful removal of possible traces of chloride and bromide. A very pure product may be easily prepared, however, by synthesis from pure hydriodic acid and purified potassium bicarbonate. 

Methanol synthesis resembles that of ammonia in that high temperatures and pressures are used to obtain high conversions and rates. Improvements in catalysts allow operation at temperatures and pressures much lower than those of the initial commercial processes. Today, low-pressure Cu-Zn-Alminium oxide catalysts are operated at about 1500 psi and 250°C. These catalysts must be protected from trace impurities that the older high-pressure (5000 psi and 350°C) and medium-pressure (3000 psi and 250°C) catalysts tolerate better. Synthesis gas production technology has also evolved so that it is possible to maintain the required low levels of these trace impurities. 

Impurities in illicit morphine or heroin samples are important in establishing the manufacturing source of the drug. A16,17-Dehydroheroinium chloride (208) has been found(32l) in trace amounts in illicit heroin and may also be formed as a post-injection artefact during GC analysis of heroin samples. A synthesis from morphine-N-oxide by treatment with excess of hot acetyl chloride has been effected and 208 converted to 16-cyanoheroin (209) with aqueous KCN. 

Lupinine Group.—A new lupinine ester (1) obtained from seedhngs of Lupinus luteus contained traces of the c -isomer, which could be obtained from the trans-derivative by irradiation. The structure of the alkaloid was established by hydrolysis and by synthesis from (-)-lupanine and trans-4-acetoxycinnamyl chloride. ... 

The solvents used in synthesis are also likely to involve a number of impurities that may extend from trace levels to critical quantities that can react with various chemicals used in the synthesis, to give rise to other... 

Ammonia Equilibrium. In school experiments, it is possible to quantitatively decompose ammonia gas with the help of a nickel catalyst into its components. From 50 ml ammonia, we can get 100 ml gas, namely 25 ml nitrogen and 75 ml hydrogen (see E6.7). However, it is not possible to reverse the procedure under normal pressure, i.e. to achieve the ammonia synthesis from the elements. The volume-temperature diagram (see Fig. 6.10) confirms this one does not get any noticeable traces of ammonia at a pressure of 1 bar. In contrast, ammonia can almost be completely produced from the deployed gases at 200°C and a pressure of 1000 bar ... 

The history of C-H amination can be traced to the earliest work of Hofmann involving the reactivity of /V-bi omoamines. chemistry later recognized by Loffler and Freytag for its potential to facilitate pyrrolidine synthesis from simple acyclic precursors [11]. The intermediacy of both haloamine and aminyl radical in this stepwise oxidation reaction is now generally accepted, as is the hyper-reactivity of... 

In peptidase-catalyzed peptide synthesis the solubility of the starting components dramatically influences the course of the synthesis. From the ideal medium, water, the spectrum of solvents ranges from water-miscible organic solvents and aqueous-organic biphasic systems to monophasic organic solvents with trace amounts of... 

The DIBAL-H reduction of 48 produced a mixture of the alcohol 49 and aldehyde 8. We were unable to halt the reduction completely at the aldehyde stage even by reducing the temperature to -100 °C. Fortunately, oxidation of the mixture proceeded without detriment to the integrity of the aldehyde component. Aldehyde 8 was purified by a tedious chromatography and was a stable compound, though unfortunately not crystalline. Several by-products were isolated (55-57). These are very probably formed from traces of the corresponding side products carried through the synthesis from the previous steps. 

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