In this paper, we present a privacy-preserving approach for machine learning-based retrosynthetic model training, the Chemical Knowledge-Based Framework (CKIF). Traditional retrosynthetic model training involves aggregating reaction data from multiple sources into a single point, which increases the risk of corporate confidentiality leaks. CKIF enables distributed training through iterative chemical knowledge-based aggregation of model parameters without disclosing proprietary reaction data from individual companies. The chemical properties of predicted reactants are used to quantitatively evaluate the observable behavior of individual models, which is then used to determine the weights used for model aggregation. CKIF significantly outperforms several strong baseline models on a variety of reaction datasets.