Insect Behavior Modifying Compounds

The invention is illustrated by the following Examples.

The aldehyde or ketone (100 mmol), triethylorthoformate (125 mmol) and absolute ethanol (40 ml) are mixed together. The catalyst (200 mg) is added and the mixture stirred at room temperature under nitrogen for 24 hours. The reaction is monitored by gas-liquid chromatography on a 5'.times.0.25" glass column of 10% OV-17 on Chromosorb W at 170.degree. C. with a 20 ml/minute N.sub.2 flow. The ethanol is removed under vacuum, hexane (200 ml) is added and the solution is partitioned with saturated aqueous NaHCO.sub.3 solution and the hexane layer removed and dried over Na.sub.2 CO.sub.3. After removing the solvent, the residual oil is vacuum distilled to give the required diethyl acetal or ketal.

The diethyl acetal or ketal (10 mmol) and benzyl alcohol or substituted benzyl alcohol (30 mmol) in benzene (100 ml) are heated slowly with catalyst and the benzene-ethanol azeotropic mixture is distilled out until the temperature reaches the boiling point of benzene. The reaction mixture is then cooled, basified with anhydrous K.sub.2 CO.sub.3 and concentrated. The residue is vacuum distilled to remove the excess alcohol (in the case of benzyl alcohol) or extracted with hexane several times (in the case of substituted alcohols such as o-nitrobenzyl alcohol or 3,5-dimethoxybenzyl alcohol). The residue from the vacuum distillation or the hexane extraction concentrate is purified on an alumina column, eluting with hexane containing gradually increasing amounts of ether. The apprpriate fractions are combined and evaporated to give the required dibenzyl or substituted dibenzyl acetal or ketal.

The diethyl acetal or ketal is prepared by the above general procedure from (Z)-11-hexadecenal, (E)-and (Z)-citral in admixture and heptan-2-one using NH.sub.4 Cl as catalyst in the first two cases and TsOH in the last. (Z)-1,1-Diethoxyhexadec-11-ene is obtained in 61.5% yield and has a b.p. 118.degree.-120.degree. C./0.05 mm, n.sub.D.sup.20 1.4475; (E)-o and (Z)-1,1-diethoxy-3,7-dimethoxyocta-2,6-diene in admixture are obtained in 83.6% yield and have b.p. 68.degree.-70.degree. C./0.2 mm, n.sub.D.sup.20 1.4511; 2,2-diethoxyheptane is obtained in 71% yield and has b.p. 88.degree.-92.degree. C./18 mm.

The details of the "transacetalisation" reactions effected between the above three products and each of benzyl alcohol, o-nitrobenzyl alcohol and 3,5-dimethoxybenzyl alcohol are given in Table 1, the products being designated by the FIGS. 1, II or III according to the carbonyl compound involved and by the letters c, d or e according to the alcohol involved. The catalyst used was an amount selected in the range of 3-100 mg of p-toluene sulphonic acid for all of the products of types I and III, 100 mg of ammonium chloride for products II and IId and 100 mg of oxalic acid for product IIe.

(Z)-11-Hexadecenal is prepared from (Z)-11-hexadecenol which is obtained from 11-hexadecynol (this being obtained in turn by the reaction of 10-bromodecan-1-ol and 1-hexyne), the procedure being based on that of Nesbitt et al, J. Insect Physiol., 1975, 21. 1983. (E)-citral in admixture with ca. 40% of (Z)-citral, and heptan-2-one are obtained commercially.

All three are obtained commercially.

The aldehyde (2 mmol), o- or p-nitrophenylethylene glycol (4 mmol) and p-toluenesulfonic acid (20 mg) are dissolved in benzene (50 ml) and the solution is refluxed under nitrogen in a Soxhlet apparatus having the extraction thimble filled with dehydrated MgSO.sub.4. The reaction is monitored by thin layer chromatography on silica gel, developing with hexane-ether. After six hours, the reaction mixture is cooled and the pricipitate filtered off. The filtrate is washed with saturated aqueous Na.sub.2 CO.sub.3 followed by brine, and is then dried over MgSO.sub.4. After removing the solvent the residue is chromatographed on Al.sub.2 O.sub.3 (neutral), eluting with hexane containing gradually increasing amounts of ether. The appropriate fractions are combined and evaporated to give the required product.

The diethyl acetal or ketal (10 mmol) and o- or p-nitrophenylethylene glycol (15 mmol) in benzene (100 ml) are heated slowly either without or with catalyst (100 mg) and the benzene-ethanol azeotropic mixture is distilled out until the temperature reaches the boiling point of benzene. The reaction mixture is cooled, basified with anhydrous K.sub.2 CO.sub.3 and concentrated. The residue is extracted with hexane several times and the hexane extracts are chromatographed on an Al.sub.2 O.sub.3 column, eluting with hexane containing gradually increasing amounts of ether. The appropriate fractions are combined and evaporated to give the required product.

The details of the 1,3-dioxolane preparations effected by the above general procedure A for (Z)-11-hexadecenal and the above general procedure B for (E)- and (Z)-citral in admixture (with a NH.sub.4 Cl catalyst) and for heptan-2-one (with no catalyst) and each of o-nitrophenylethylene glycol and p-nitrophenylethylene glycol are given in Table 2, the products being designated by the FIGS. 1, II or III according to the carbonyl compound involved and by the letters f or g according to the glycol involved The 1,3-dioxolanes derived from (Z)-11-hexadecenal and heptan-2-one are a mixture of two diastereoisomers whilst those derived from (E)-citral in admixture with (Z)-citral are a mixture of four isomers.

These or the diethyl acetal or ketal derived therefrom are obtained as described under Example 1.

o- and p-Nitrophenylethylene oxide are prepared from o- and p-nitroacetophenone through brominaton, reduction and dehydrobromination according to Guss and Mautrier, J. Org. Chem. 1951, 16, 887 and Guss, ibid, 1952, 17, 678. The oxide (2.9 g, 17.6 mmol) and potassium carbonate (1.7 g) are dissolved in 50% aqueous 1,4-dioxane (130 ml). The reaction mixture is refluxed at l10.degree. C. with magnetic stirring for 24 hours, the reaction being monitored by t.1.c. as described above. After cooling the reaction mixture is neutralized with 2N HCl, concentrated under vacuum, extracted with ether, and dried over MgSO.sub.4. After removing the ether, the residue is crystallized from benzene-hexane to give, as light brown crystals, o-nitrophenylethylene glycol in 69.4% yield having m.p. 91.degree.-92.degree. C. or p-nitrophenylethylene glycol in 51.3% yield having m.p. 80.degree.-92.degree. C.

Irradiation was carried out over a CAMAG universal HV lamp emitting at 350 nm. The compound to be irradiated was dissolved either in hexane or 80% aqueous dioxane and diluted to 1 mg/ml concentration, the sample then being sealed in a borosilicate glass tube under nitrogen An irradiation time of 24 hours was employed for the experiment. The recovered carbonyl compounds were identified by co-injection with authentic samples and quantitatively analysed on gas-liquid chromatography using a 7'.times.0.25" glass colum of 10% carbowax on Chromosorb W at 200.degree. C. for the detection of (Z)-11-hexadecenal, at 190.degree. C. for the detection of (E)-citral and at 140.degree. C. for the detection of 2-heptanone. In all cases studied, no carbonyl compounds were recovered from the control (which was wrapped with aluminium foil). Those samples more sensitive to UV were examined in hexane under a 20W daylight lamp over periods of from 3 to 24 hours.

The results obtained for the various adducts identified in Tables 1 and 2 are shown in Tables 3 and 4. It will be seen that no recovery of the carbonyl compound was detected in the case of the acetals and the ketal derived from benzyl alcohol, 3,5-dimethoxybenzyl alcohol and p-nitrophenylethylene glycol. However if only small amounts of carbonyl compounds were formed during UV irradiation these would most likely be lost by photolysis and their release would be undetected. Such photolysis presumably accounted for the full theoretical yield not being observed for any of the released carbonyl compounds. Moreover, failure to achieve release under these conditions does not mean that the same adducts will not release the carbonyl compound over a longer period in the field and that a slower rate of release may not be more appropriate for practical use of the adducts in the field.

Comparison between the persistence of (Z)-11-hexadecenal release from the underivatised material and the adduct If of Table 2 on glass was studied employing a method similar to that of Baker et al, J. Chem. Ecol., 1980, 6, 749. Either (Z)-11-hexadecenal (0.10 mg, 0.42 umol) or the adduct If of Table 2 (0.17 mg, 0.42pmol) was dissolved in hexane (100 .mu.l) and placed on a glass disc (16 mm), in duplicate. After irradiation (20W daylight lamp) for 17 hours each disc was suspended in a closed 250 ml round-bottomed flask for a further three hours irradiation. (Z)-11-hexadecenal released from the discs onto the inner walls of the flasks was quantified by washing the flasks with portions (10 ml) of hexane solution of octadecane (0.01 mg/ml) as internal standard and then analysing the concentrated washings by gas chromatography using a 5'.times.0.25" glass column of 10% OV-17 on Chromosorb W at 170.degree. C. with a 20 ml/minute N.sub.2 flow.

It was found that the adduct If continued to release (Z)-11-hexadecenal (0.9 ug, 9%, in three hours) after the initial irradiation of 17 hours, none of the compound being obtained from the underivatised sample after this period.

Lures were prepared from polyethylene closures (WP/5, Fisons) containing one of:

(i) (Z)-11-hexadecenyl acetate (10 .mu.g).

(ii) (Z)-11-hexadecenyl acetate (10 .mu.g) +adduct Id of Table 1 (33 .mu.g, equivalent to 15 ug of (Z)-hexadecenal).

(iii) (Z)-11-hexadecenyl acetate (10 .mu.g)+adduct If of Table 2 (25 .mu.g, equivalent to 15 ug of the aldehyde).

The lures were hung in brown cardboard traps (Oecos), triangular in cross section (side 100 mm, 176 mm long) with a removable sticky card base. The traps were placed horizontally in five groups of the three randomly arranged lure types in a N/W line with 15 m spacing and the traps aligned E/W in Brussels sprouts at crop height, 10 June 1982, Bedfordshire, UK. Diamondback moths, Plutella xylostella (L)., were counted each week and the sticky card changed each week for four weeks.

The weekly catch from the total of five groups of traps for each type of lure are shown in Table 5.

It will be seen that the acetate alone caught few moths but that when the adducts were employed with the acetate there were good catches which persisted for the four weeks of the test. These catches were of a similar magnitude to those obtained in nearby tests using fresh lures containing the equivalent amount of the underivatised aldehyde and the acetate, but whose attractancy did not persist for longer than two weeks.

In 1983, similarly good catches were obtained with lures of types (ii) and (iii) containing adducts Id and If, respectively. Additional experiments were carried out using lures containing instead one of the adducts Ic and Ie of Table 1 and Ig of Table 2, in each case in an amount equivalent to 15 .mu.g of the aldehyde and together with 10 .mu.g of (Z)-11-hexadecenyl acetate. The catches recorded with these three additional types of lure were relatively low, being less than 5% of the catches recorded with the lures containing the adducts Id and If. This result does, however, contrast with the zero recoveries reported for these adducts in Table 3. Moreover, when the amounts of the adducts Ic, Ie and Ig were increased tenfold, the catches increased to 30% (for Ic and Ie) and 15% (for Ig) of those obtained with 15 .mu.g aldehyde equivalent amounts of the adducts Id and If, and the persistence of the adducts Ic, Ie and Ig was found to be greater so that catches continued to be recorded using the adducts Ic, Ie and Ig after they had ceased with the adducts Id and If.