Is it typical to place code in an escrow account when purchasing a company?

One company wants to buy 10% of another company (ours), and one of the conditions of purchase requires the placement of code in escrow. With any change in the company, which sells 10%, including bankruptcy, change of major property owners, etc., buying company wants to get the code.

Among the events that automatically trigger the sending of code called a lot of other details, such as non-infringement of patents (but no one is immune from patent trolling), etc.

Is this practice typical? If so, at what percentage of purchased property?

Requesting code escrow is not that unusual. Sometimes a customer will request it. For example, if your service is vital to the operations of a customer, that customer may request code escrow so that its business doesn't get disrupted if your company goes out of business.

For this kind of thing, the devil is in the details. In your case, one very important detail is the preconditions for when the other company gets access to the code in escrow. You want those preconditions to be very high while the other company will want them to be very low. Unfortunately, you really need a lawyer to help you negotiate that.