The present invention relates to a delivery system in the form of a dynamic mixture obtained by reacting together, in the presence of water, at least one hydrazine derivative with at least one perfuming, flavoring, insect repellent or attractant, bactericide and/or fungicide aldehyde or ketone. The invention's mixture is capable of releasing in a controlled and prolonged manner said aldehyde or ketone in the surrounding environment. Furthermore, the present invention concerns also the use of said dynamic mixtures as perfuming ingredients as well as the perfuming compositions or perfumed articles comprising the invention's mixtures.